Isn't it kinda crazy that Proton is used not only as a way to play Windows games without Linux support, but also as a specific target because it's more stable than Linux? (Stable as in "works predictably like expected", not as in "doesn't have bugs")

Linux as a target is super difficult due different kernels, drivers, distros, DEs, libraries, services and so on. Proton just abstracts all that away and thus is a much easier target to develop for.