There is the extra complexity of differences between distros and such, but it seems like the biggest reason is simply that companies don't dedicate the same resources to a Linux version that they do to Windows, due to it being a much smaller market.
Alright, thanks. I just want to make sure I'm not walking into some weird pitfall where suddenly some very niche Linux distro has some core graphical issue to address. I know I can't optimize for every flavor of Linux under the sun.
Just optimise for the Steam Linux Runtime, it's cross-distro compatible.