Earlier quoted context omitted.
They have done that. They gave some cash money to CodeWeavers, the company that created wine. It's called the Game Porting Toolkit: https://developer.apple.com/games/game-porting-toolkit/
That's the problem I think: porting. As I understand things, proton allows windows games to just work (pun intended) on Linux. No porting, no rebuild - just download and run. Who is going to bother doing all the extra work to port their game for Mac?! Time and time again there have been loads of articles on here over the years with developers saying it is simply not worth the hassle to support Linux and Mac.
There is a relatively easy way for a player to use GPTK to run games from their Steam library on Mac.
Here is how to use Apple's Game Porting Toolkit to install Wine & Steam.
1. Go to https://github.com/installaware/AGPT and download & run the installer
2. Go to https://store.steampowered.com/about/ and download the installer
3. Open a Terminal, run mkdir Games && gameportingtoolkit ~/Games Downloads/SteamSetup.exe
4. Follow the instructions at https://www.applegamingwiki.com/wiki/Game_Porting_Toolkit#Sh...