You'd think, but a lot of mainstream engine-based games that could "easily" have a mac port never get one, even an unofficial one offered as totally unsupported. Look at Among Us for example. Not by any stretch a high-end game. It runs on Windows, Android, iOS, a bunch of XBoxen, and probably other consoles. I bet the developer could spit out a working native macOS version with the push of a button, but so far hasn't.
Kerbal Space Program is another example. When last I checked, they did have a native mac version, but it was hamstrung in some way--I think it was limited to 32-bit or something.
I can't imagine these examples are actually a huge amount of effort to make happen. As a fan and programmer I'd be willing to do it for free.
A lot of games did drop off the Mac when it moved to 64-bit only though.