I don’t know for sure, but I suspect a lot of the work is spent sussing out weird edge cases with different binaries. This is tedious, thankless work, but it is necessary to have true Windows compatibility.
Wine and Proton have gotten so good that I don’t bother even checking compatibility before I buy games. The game will likely run just as well or better than on Windows and it is so consistently good that it’s not worth the small effort to check ProtonDB.
I do wish that they would get Office 2024 working on Wine. This isn’t a dig at the Wine devs at all, I am sure that it’s a very hard problem, but if I can get that then I will have even more ammunition to get my parents to drop windows entirely.