The problem is that it ISN'T a fee for services as it should be. Their platform power means that they can levy a tax, and they don't feel the need to do anything on exchange for that.
It is rent extraction which always feels like bullshit because it is. Competition is supposed to be the counterbalancing force but it barely exists here.
Yep, I'd hypothetically economically gladly build an alternative app store charging "only" 5% on app revenue. The blocker would be that Google has a hold on what store is installed by default on Android. Apple even more so. This is hardly a fair market.