I thank goodness I haven't been subjected to (mobile) Apple for many years in order to speak to what they "allow" and don't nowadays, but the short answer is that I want to *fucking own* the hardware I pay fuckloads of money to purchase
Also, while I was typing out the "I want f-droid.org for iOS" I realized there is a pragmatic answer: I want to build and distribute apps without having to pay for the right to do so, not because I am stingy but because paying is gatekeeping. Do you know how much the Joplin devs have to pay Google to put this .apk link here[1]? $0