This is why it’s mainly larger developers that care about their community that implement Linux support. Take valve for example. Wonderful company that cares about their playerbase more than the average game development team. They have Linux support on almost all of their games as far as I am aware. Bungie is a decent company but most of their community doesn’t want to play on Linux anyway, so they won’t bother with it. However most teams that are smaller or care more about money than players won’t do it.

Yes, they do. There is more than just the engine at play on compatibility. The main reason is actually usually the anti cheat.