APIs are the last reason there aren't 'major' games on macOS. You've got architecture changes; PPC to Intel was a big loss of game compatibility, and then again when x86-32 support was removed from OS X nuked most of a user's Steam library.

And there's the chicken/egg problem of gamers just not being present in large enough numbers on macOS. The platform already has a fairly small marketshare in the overall PC space, the number of gamers are vanishingly much smaller; Steam stats put macOS at 1.58%, less than Linux.

https://store.steampowered.com/hwsurvey

All of the major game engines support Apple's Metal, so API compat from that perspective isn't an issue.