Some of us just prefer to be in Linux [0]. And either way, you're likely using your computer the vast majority of time for non-gaming related stuff. I for one don't want to dual boot to play for a few minutes, or really have to do anything in Windows, games or not. As a commenter below points out, it's a choice.

[0] https://boilingsteam.com/my-journey-to-finally-ditching-wind...