Developers need to optimize and debug their game for each console. Xbox/PS are completely different platforms (UWP vs heavily customized BSD) so fixes don't transfer over. Adding another incompatible target with new store guidelines and system APIs adds a lot of work so Apple would have a hard time convincing them.
Now add the perception that Mac users don't play games and Apple devices are made for people already in their ecosystem. The only way they could gain market share is competing with Steam Machine as a more open platform, but without a giant library of existing games.
Now add the perception that Mac users don't play games and Apple devices are made for people already in their ecosystem. The only way they could gain market share is competing with Steam Machine as a more open platform, but without a giant library of existing games.