That's exactly what Apple is doing - in this case protecting their ecosystem from providers that use undocumented APIs and MDMs whose business model is fingerprinting customers and selling to advertisers.
What exactly do people expect of Apple here? Apple gets criticized if it doesn't take a hard line on customer privacy, but when it does exactly that it is abusing monopoly power and needs to be regulated and broken up.
If people want third party app stores that's fine, but let's be very clear about what that means. It is going to come with compromises in terms of crappy UX, dark patterns, privacy violations, private APIs and all sorts of stuff that users pretty much hate.