Apple insist on having their own apis and they don’t maintain compatibility for older software for very long, these 2 facts explain things fine on their own. Game devs don’t want a major support burden, they’re happy to patch here and there but constant dropping of apis or even architectures is a lot to handle. The bigger impact is that macOS ends up with a lot less old games that still run, if you need a critical mass of games to become a gaming platform, that constant bleed of legacy games will always slow macOS down.

As for gaming specific features, Metal is a perfectly fine api whose only real problem is that it’s different from the other platforms. Maybe not the best, but certainly not terrible. They also have a really nice capability floor, it’s practical to make a modern game work on any Mac from the last X years (maybe the neo complicates that a bit).

There’s probably a few gaming specific capabilities they could improve on, mouse input especially, but that’s never been the real issue.