Games and niche software for the most part.

Yeah, compatibility on Linux is better now, especially with Valve implementing Proton so games would run on the Steam Deck.

But there are still incompatible games, and non-Windows operating systems are generally not a priority for many game developers. So, you have to hope that either Valve or the community have found a way to make them run on other systems.

And then there's the aforementioned niche stuff. Yes, your games may be compatible with Linux, but what about the tools needed to mod them? Plenty of modding and ROM hacking communities only develop for Windows, so anyone looking to get involved in those scenes has no real choice other than to use Windows. Wouldn't be surprised if plenty of non-gaming communities made heavy use of tools from the days of Windows 95 or MS DOS too, whose creators haven't bothered to update them in years or who have no interest in porting them to Linux in general. Bonus points if the tool is closed source freeware from some site that looks like it was made in 1995.