Ten years ago when I was younger and a lot more naive, I would've totally agreed with you. Heck, if Apple did this 10, 15 and 20 years ago, maybe things would be different now - but as it stands, Windows has a lot more to offer than just games.
Fact is, because there's so many installs of Windows out there, there's a HEAP of help on the internet for problems you stumble across, it supports virtually all the hardware out there conceivably able to be plugged into a machine and more importantly, for me - is the little programs, thousands upon thousands of convenient, half decently designed tools which MacOS and Linux simply don't have.
I'm talking data de-duplication searching tools, multi-monitor window managers, downloading / p2p tools, media players, media encoders etc. There's just heaps and heaps of little things you probably wouldn't realise if you switched to Mac or Linux for the first week but suddenly in the second week, you'd be googling for 2 days trying to find that one little tool to do that one little thing which simply doesn't exist, or the only tool close to it is awkward and ghastly.
This isn't to Windows credit, Windows didn't get this stuff due to it being designed better or something, it's simply because there's more Windows installs. If linux or MacOS ever did take over, great, those tools would come - but for the time being, depending on how you use your computers, there's few reasons for a Windows guy to move to Linux or MacOS.
(oh and FWIW Windows has become a pretty stable OS nowadays, I see applications crash, sure -but the whole desktop crashing is exceedingly rare)
TLDR: Games alone ain't gonna cut it to lure people away. Heck I barely play them anymore myself.