I think it's a network effect thing as much as anything else. If it's good enough to get people playing games on their macs at all (even if at relatively sub-par settings), that builds the market, shows there are people willing to spend money on games to play them on their macs.

Then at that point games developers might be more inclined to give the platform explicit support.

Otherwise it's a bit of a chicken and egg situation: people aren't playing games on their macs because the library isn't there, the library isn't there because no developers will support a platform where there aren't gamers and so on.