The "perfectly fine game store built into Mac" wouldn't even accept many of the games currently available on Steam. Anything with the "Adult Only" rating would just be outright rejected.
Obviously you also wouldn't be able to install the games you bought on there on any device that didn't have an Apple logo. Sharing the same game library between Windows, macOS and Linux? Nope, buy them again.
You might also have to kiss goodbye to cloud saves. The macOS App Store version of Resident Evil 4 doesn't support cloud saves between macOS and iOS devices whereas the Steam version has cloud saves.
And this is the state of Apple's game store when they are facing competition.
Obviously you also wouldn't be able to install the games you bought on there on any device that didn't have an Apple logo. Sharing the same game library between Windows, macOS and Linux? Nope, buy them again.
You might also have to kiss goodbye to cloud saves. The macOS App Store version of Resident Evil 4 doesn't support cloud saves between macOS and iOS devices whereas the Steam version has cloud saves.
And this is the state of Apple's game store when they are facing competition.