Nobody buys an iPhone, iPad or Mac just for gaming. You seem to be focusing on only new users and buyers and forgetting the current customers. It's about the huge user base and potential profit for game devs. It would be foolish to ignore billions of people just because it's cheaper to buy a PC, console or Android.
Here are some iPhone
stats. There are over 1.5 billion active iPhone users in the world and Apple has sold over 2.24 billion iPhones. Add to that millions of sold Macs and iPads each year. All using Apple Silicon. Even if your game would be expensive to port to Mac alone you could first port it to iPhone/iPad and make good profit and then easier port it to Mac since they all basically use the same HW architecture. Feral has done some excellent AAA ports to iPhone, like Alien Isolation. The potential is huge but many devs want rather make money on microtransactions on the mobile platform than developing for Mac. That's why many don't even allow their iPhone games on Mac even if it would work just fine.