Why is Steam so successful?

3 words: Half. Life. Two.

its fanatical userbase. Valve got there first with steam and grabbed their large userbase first before anyone else could. Seriously, that is ALL there is to it, steams users. valve can do as little work as it wants, and its fans will just stay rabidly loyal.

Huge discounts, economy(gifts, keys, items, etc), and 90%(made up on the spot, but you understand) of all games are there

They have the best customer service in the industry! Duh!

Steam has been successful only because the entire community is waiting for HL3. We buy everything to fill up our free time that will be completely dedicated to HL3. Steam knows this so it is why they don't want to release despite HL3 is already developed. #tinfoilhat

The real question is: Why the hate on anything that isn't Steam?

In the beginning, it was required to use Steam in order to play Counterstrike 1.6, Team Fortress Classic, etc., after won.net shut down. So right off the bat it was extremely popular, albeit shitty.

Because they let you redeem serials purchased at other retailers and have developed community functions. No other "drm" (Uplay, Origin, Desura, whatever) has both qualities to the extent Valve's Steam services do.

People want to bless Gaben by giving him their money.

Steam is easy

They've been at it for a long time and have learned(and still learning) from their mistakes. They've become the go-to digital game retailer for consumers due to their deep discounts and easy-to-use platform. And it's the go-to DRM for companies because of the massive exposure and pull Valve has on the PC market. But when it comes down to it, Valve just had perfect timing when they pushed the digital gaming market.

because it's a privately held company and the owner happens to be the Gaben

It came with Counter Strike 1.6, then a year later, BOOM!, Half Life 2, and due to that success third party publishers supported Steam, another thing is Steam summer sales, left 4 dead, allowing mods with their games, community or forums for almost any shit you want, etc.

Because of people like you, think about it :)

Because STEAM was the very first of its kind. Simply that. Timing in business is everything.

It came first plus was shoved down the throats of people who just wanted to play some great VALVE videogames.

Good sales over a huge selection. The client is free of bloat and is pretty straightforwards. The EULA / terms of services aren't horrendous, and it's provider (Valve) has a good track record and have generally been open and honest with the customer base. It also started up when there were no majorly unified online platforms, and filled the gap nicely.

Nothing is stopping others from stepping up and challenging Steam, but nobody seems to be bothered. There are good sites for sales like GreenManGaming, but that lack the unified nature of Steam's client. There are people trying to get into the online distribution thing like Origin, but they typically come with terms of service or EULAs with rancid sentiments in them, bad pricing, clunky clients, or just a simply poor selection. If Steam had some real competition, it would be a good thing. They could drive one another to excel.

Two words. Orange box.

The program offers an immense variety of games, automatically updates them so you don't have to mind patches, seamlessly serves up DLC, and offers chat, game invites and free multiplayer servers. It's a fundamentally good platform that has a lot of bugs, but not nearly enough to outweigh its positives. On top of that, its frequent sales attract deal-hunters, and so over time people begin using it as the hub for their games. The result? It doesn't have to compete to become a monopoly because consumers begrudge developers who don't use it. It's a game-home.

Because Valve always offers Quality, Good prices an great offers.
Allowing others developers to sell on Steam its great for players, they dont need to have lots of accounts on lots of stores. They even sell games with Origin!!, isn't that cute?.. Origin its not a threat for Steam.
Most of the crappy games on Steam are here because people, asked for them on Greenlitgh.... and lots of them, because they where "free".

And of course, Steam is soooo succesfull because Gaben its God.

Sorry, my english is not very good

games for linux, steam sales, free games and especially by the COMMUNITY

Promotions, small prices that make people buy the games
A lot of people in steam just buy games because they are cheap, and never play them, so steam makes people buy games they would pay and play, and games that they wouldn't play or pay unless it is in a small price

Steam is used to play video games but it offers much more, the customizable homepage, the friends & community, forums, groups etc.
it's very nice to meet and group up with people.