What makes you play Open World RPGs for 50+ hours?

Witcher 2 isn't even an open world rpg. Skyrim is open world.

With Oblivion for example, I just like exploring and doing random side quests. Dark Brotherhood is fun, the Arena was good. It was only when I travelled to another town for a side mission that I was suddenly reminded of the main quest which I'd hardly touched.
I don't really play too many open world RPGs, but I don't know. I just can get into them sometimes.

Tons of different stuff to do, big world, lots of missions, secret or just normal places to explore, lots of items, lots of mobs, different classes, story moments that depend on your decision, mods. Try Skyrim.

Mostly that keeps me playing is the story.

Thats the reason i dont play rpg games, if i turn addicted to the game i will play 24/7. I always avoid playing that kind of games

I guess these games create illusion of accomplishment when one finish a quest more if they are'nt happy with his life (IM NOT JUDGING, DON'T TAKE THIS THE WRONG WAY)
But thats what im thinking who knows

I love leveling up things before I finish the main story. This includes exploring and gathering for the things I need. I do side quests too but usually at the same time as the main story.

As NB264 Stated, The Witcher 2 isn't open-world; there are plenty of invisible walls to keep you where they want you, which makes it a closed-world RPG.
True open-world RPGs (eg. The Elder Scrolls series) have very few invisible walls... In fact - in some games - the invisible walls at the border of the map(s) can be disabled, allowing you to travel further; not that there's much out there! :)

can only really speak for fallout new vegas and to a lesser extent fallout 3 but its exploring the whole game and trying different play options, i mean new vegas ive only tried different combos of NCR runthroughs as i cant face even roleplaying as a slaver, its got flaws but its so fun and i only uninstalled due to needing the hdd space, soon as i replace my data drive ill mod new vegas again and spend silly amounts of hours in it and im looking forward to bethesda doing a fallout IV at some point

MODS, MY FRIEND, MODS !

I only play long-form games if they can keep my attention. Same with you, Witcher 2 didn't quite do that for me. Although Deus Ex Human Revolution, Fallout New Vegas, Borderlands 2 and Watch Dogs did.

Loot-o-mania. Hard sickness. I get it after watching Adventure Time.

For starters, most Open World games like Fallout or Elder Scrolls have significantly more than 10 hours worth of main story (thats not accounting for sidequests).
On top of that they often have dozens of hours of sidequests aswell.
Keep in mind, the playstyle of these games isn't to finish it in one sitting. The #1 rule is to save early and to save often.
Unless you set a personal survival challenge limiting you from that (but thats another story).
These games are not designed to be done with in a week. Even if you have the week off and are doing nothing else, you can be sure that you'll have something else to explore after that full week of play.

Even if you don't play through all of those quests on a single character, they offer replayability on a second or third character playthrough.
You might play your first character as a good guy and second as a bad guy. Or you might try a completely different combatstyle.
If you're looking at Mass Effect you might try another class or allignment.
If you're playing Baldur's Gate/Neverwinter Nights you can try a different class.

That alone often already accounts for dozens of hours of gameplay, quickly running upwards of 40~50 hours if not reaching in the 100s.

Now ofcourse it depends on the player whether they are a completionist and want to do ALL of the sidequests. Or whether they are an explorer and just want to find all the little secrets (of which there often are a ton).
Many of these games also offer modding. Elder Scrolls, Fallout, Neverwinter Nights and others have extensive active modding communities.
Providing new toys, maps, adventures and other content to play with.

And thats the thing about openworld games. They not only provide you a ready-made adventure, but also offer you a sandbox in which you can create your own adventure. Which obviously is not for everyone.
A lot of people either get 'lost' in the freedom and prefer a more linear approach as if on rails, just following where the story takes them rather than having free control. Others just don't see the appeal and others again feel they do not have the time to play that long.

Personally I prefer openworld games and RPG's in general over mostly every other genre. Not only do these games tickle a certain itch for freedom and relevant choices. But they also provide significant content - more bang for your buck if you will.
I've never seen the appeal towards generic multiplayer, after 10~20 hours of say Battlefield: Bad Company 2 I got bored and removed it.
I can't stand Call of Duty and most of the other ones (Team Fortress, Counter-Strike etc) just don't appeal to me at all.

There is another reason to play openworld games, which is survival. Often these games (Elder Scrolls and Fallout do it either through core options or through mods) offer a more survival oriented method. Its harder, you need to play the game more realisticly.
Combat often is cranked to the max you need to eat, sleep and drink and depending on your preferences you can even set the world to kill you (environmental hazards like rad/chemstorms in Fallout or frostbite in Skyrim).

I hope this answers your question - it really differs from person to person what they get out of an openworld game.
And it differs from game to game what options are available to you. But you can be assured of one thing - almost all of them offer you a significant number of hours playtime and are value for their money without having to repeat the same map repetatively online.

Well not a fan, but after winning a Skyrim copy here and start playing... I realized how boring the real life is and BAM, 75 hours in, and I don't even make quest, just sit for hours reading books I find, more th... xD, but rec if you play skyrim: Unnoficial Skyrim Patch + SKSE + SkyUI + Advanced Follower Tweaks.

Everything but the main story.

I. Never. Finish. It.

Personally these open world games were so good and interesting to me because usually I was watching someone else play it or it had someone to co-op with in it that I could just at any time jump in and play. Namely in this case I loved playing GTA Vice City and San Andreas with my cousin on the PS2, the shenanigans we had were endless and we used to just switch between missions or when one of us got bored. lol

The other was with my dad, I used to watch my dad play all these awesome nitty gritty kind of games usually with a dark apocalyptic kind of setting or umm what's the word like has a sort of barbaric feel to it lol. Games like Nox, Torment and ofcourse the early Fallout series were all great games to just watch by in the passenger's seat and have a feel of playing the game but not really.

I haven't tried Witcher 2 yet, but if you want to experience a good playthrough of any game really in particular open world or not, I suggest maybe getting or looking for a gaming buddy, if you don't already have one. Maybe a close relative or someone.

[Sorry for the long post and thanks for giving me the chance to let some of that out, I think I needed to.]

I keep playing such games, because I really like them and there are things left to do for me.
After finishing the main story, there are many side missions and I'll try to complete them all.
Then there might be achievements and this stuff. Getting all is probably really hard and you most likely won't get them all, but you can do it one by one so you're getting nearer to the 100%.
I also play to get better, i.e. maximize my gear and skills and stuff if that's possible in the game.
In many games, there's also PVP and it can also be very fun.
There are many aspects which make me play a game for a long time and it's even much funnier to play together, in a team or against each other.

"What makes you play Open World RPGs for 50+ hours?"

Nothing. Just main story in my case... sometimes story related side quests.

fallout 3 - house- cigarettes
the main rooms were lined with cartons from floor to ceiling all neatly stacked, tables/counters covered in loose cigs, single packs in a huge pile in every room....

it was a house of cigarettes.......

Becaus the voices go silent for a while.

no they don't yes they do no they don't

Probably the lack of plot and copy-pasted enviroments, like in all The Elder Scroll games. That's why I prefer RPG games like Gothic or The Witcher.

I much prefer mmos to open world single player games.

Lore everywhere, interesting NPCs, cool side-quests, tons of things to find. Open-world RPGs are really cool when they're done well, like Fallout: New Vegas, Arcanum of Steamworks and Magick Obscura or Mount & Blade: Warband.

Escapism

I graduated recently with a report about gameplay triggers and its addictive effects.
It's in Dutch, unfortunately for you.

But the main conclusions were about association identification, thus progressing 'yourself' via the character. Also, collecting items/achievements is a major replayability trigger.