Possibly because the cost for entry to macOS is higher than with iOS. Most people are able to run a Windows computer at very little cost, and will never have any interaction with a Mac. Meanwhile, iPhones and Android phones are (broadly) on a par in terms of cost.
I once bought a load of Lego games on my iPhone 3GS, mostly for my kid to play, but with a mind to play them myself when I got a chance.
Then iPhone switched over to 64 bit, and those games didn’t. Then the games got re-released in 64 bit, as a free download for the first level, with an in-app purchase to unlock the rest of the game. A game I’d already paid for on that platform, that I could no longer play.
That still pisses me off.