But i guess the main 2 problems are:
1) Not enough Mac users which would be significant for a AAA gaming company to port their games on day 1 and get profit.
2) Apple has not taken yet gaming seriously, maybe because they have not seen a viable business model for gaming. I guess here this could change as Apple is slowly putting their feet on it with Apple Arcade (which is definitely not going to bring hardcode gamers), making iOS a good gaming platform (device stability, good GPUs and good support for 3rd party controllers) now its the first time most popular Macs are getting a good GPU. Perhaps also this is one of the reasons why they are blocking Cloud gaming.