A lot of Linux ports are not the best quality to begin with, or even if they were good once, they’re out of date, utilising old fashioned technology that may not be the best at taking advantage of modern hardware. Conversely the windows version was often better built to begin with, and the translation layers have had a huge amount of effort put into them to make them as performant as possible and utilise as much of the hardwares capacity as they can, so much so that sometimes the proton version of windows games running on Linux is actually more performant than the windows native version on running on windows!