Even putting aside the performance issue, Apple and gaming have never worked together quite well.
Apple's modus operandi of quickly and frequently deprecating old architectures and requiring app developers to constantly keep up goes down very badly with the traditional video game development model - of spending time and budget finishing up one game, releasing a few patches, then moving on to the next game with little further upkeep or maintenance of the now-done game. (Yes, games as a service is more common nowadays, but a huge number of games still go by this old model.) This model relies on long-term compatibility of old binaries on the platform being pretty stable, which is fairly true for consoles and Windows, but Apple platforms are anything but.
There are massive piles upon piles of only slightly old games that are not just unsupported but simply refuse to run on both the iOS App Store and Steam for Mac (including Valve's own back catalog!), due to the abandonment of 32-bit binary support a few versions back. And even if the developer is willing to do bare minimum upkeep work to recompile an old game and make it run on current hardware, chances are that between the time of release and now, lots of new mandatory hoops (eg. natively support a certain screen size) have been added to the app store checklist so that passing store certification requires tons more work than a simple recompile, further deterring the dev.
Perhaps you could chalk it up to the dev being lazy for not doing regular maintenance of the game, but the rest of the game industry doesn't force you to do that, while only Apple does.
