What % of your games run on Linux?

And the funny part is that I yet again forgot that Quake 4 even existed. It always felt the most forgotten id-related game ever, more forgotten than Commander Keen.

Pros

They can but they doesn't have to... programs working in Windows 7 doesn't work in Windows XP (it's same timespan between 7 and XP as between 10 and 7). Even new Firefox, Chrome, Opera etc. versions doesn't work in XP. Name any new games supporting XP or Vista (loosing support this year). Same was with ME/2000 about 6 years ago... same will be with 7 in 3-4 years.
If game requires Direct 12 - it won't work in 7. Also there are already several tools/frameworks from Microsoft and other companies which require >= Windows 8.1... and sometimes they strictly require Windows 10.

Software only for Windows 10:

• MS Office 2016
• Halo Wars 2
• Fable Legends
• ReCore
• Sea of Thieves
• Gigantic
• Killer Instinct: Season 3
• Gears of War: Ultimate Edition
• Ori and the Blind Forest: Definitive Edition
• and so on...

Progress in software requires dropping support for legacy platforms... also support for less platforms (includes different Windows versions) requires bigger stuff for testing/debugging, bigger help desks, bigger teams making fixes... to sum up more money/work hours.Unsupported is the word. No updates, no new libraries, no bugfixes, no new features, no new mechanisms, no new APIs, no new SDKs, different component versions than in other systems so devs needs to spend more time on compatibility issues and it costs money. Also new development tools (Visual Studio seems quite popular) drops support for old systems.
Also unsupported system is usually less secure system.

Cons

Of course it won't happen within a day or two - it's gradual process. People update, people change hardware (= buy computers with new systems), old software versions brings more problems (no fixes) and new are easier to use (but usually slower). On the other hand as long as you know devs will support your platform in new games and all you need works like a charm there's no reason to upgrade. It works, applications in it works, you know how to set up system, use it, you like this way and system is stable and provide proper stability => there''s no reason to upgrade.
Well, probably your next computer will come with 10 preinstalled anyways so there's no reason to rush.
Also privacy mumbo jumbo... if you don't spend enough time configuring system is major issue if you take it under concern. Default settings share lots of information about user with MS and/or other companies. Finding some hidden links (c'mon, small dark gray font on violet background where all other text is 10x bigger and in more visible is cheating!!!) and buttons takes some time and many people don't want to waste it... if you pay attention to privacy and don't want to spend some time configuring system, Win10 (and well Win8 but not as much) is a bad choice.

I just stated that once activated 10 can be reactivated even in couple of years in future, and after activating you can restore 7/8/8.1 :) Most of people are unaware of it. Other stuff - how system works, how system looks, what works on it and what does not... most of people know it... or can check on virtual machine (VirtualBox, VMware, Xen, KVM, anything) or over the net.

Just saying and trying to be helpful :)

I myself keep 10 and 7 (restored from backup - license doesn't forbid it) and spend quite a while on Linuxes anyways (they are better for work I do most of time). My company have few contracts with MS so I have no big deal upgrading for free at any time anyways.