According to ProtonDB, 40% of the top 10 games are "borked". So if Proton is a serious attempt at making everything work, why do 40% of the top 10 games still not work at all? Clearly there are some Windows APIs which WINE/Proton can't emulate yet. So now your developers have to specifically avoid those syscalls and system libraries. What if a third-party library you want to use uses those syscalls? Now you need to work with the vendor to get them changed. Okay... as if that isn't bad enough... Only 20% of the top 10 games are "gold" meaning they work 100% correctly, with some tweaks. Okay, so now you have to tell users what those tweaks are, or they might refund. Never mess with an angry Linux user! And then, 20% of games work "okay" meaning there are glitches that don't affect gameplay. But... you now have to field support calls from users who see these glitches and think their game is borked. And if you're wondering why I went with the "top 10" list and not the "top hundred", it's because most Linux gamers I've seen complaining about the lack of Linux ports are complaining about the AAA top 10 games, not the simplistic 2D tower defense games. Packaging a game that already works great in Proton is beside the point.