Through iOS devices Apple has created a market of users they are the very protective gatekeeper for.
Windows PC user market. Not locked down. Though MS has a store you have Steam, EGS, GOG, Origin, UBS etc for games alone. Let alone productivity apps.
Android market. Not locked down. Though google play store is the gorilla other stores exist. I like F-Droid.
EPICS Unreal game engine? Doesn't have a locked down market of users. It would lock the business into a payment scheme though.
Xbox, Playstation, Nintendo consoles. I fear they are similar in terms of gatekeepering to users and should be subject to whatever outcome Apple is. They seem a bit more open to begin with though so are likely to be less affected. It also makes them not the prime offender, though offenders all the same.
Ultimately, want to sell to an Apple iOS user? One choice.
Separately then, is this anti-competitive or simply smart business? I'd answer : Why not both? The business wants to make money and until the law steps in, they will do it.