There was a thread on twitter recently about how app stores would have rejected the first web browser, asking what future innovations might not happen due to them. Guess federated social media is a part of the answer.
The problem is the 'App Stores'. Think of them as retail outlets, in a mall. Do you see shady stuff going on there? Would 'The Gap' sell porn to increase profits by 15%? Of course not. And for obvious reasons. We shouldn't think of 'App Stores' as some kind of truly open marketplaces, any more than a shopping mall is. What we need is just more independent means of distribution.
Thinking about them in terms of the mall or a shopping plaza is good. However, you mistakenly compared the app store with the Gap.
The app store is the mall space, numerous apps abound, as do shops. The gap might not sell porn, but Victoria secret, Spencers, Hollywood (nights?? I can't recall) exist in the mall and might not be porn but... Some retail plazas might have an adult section. Best buy or Fry's at one point had adult magazines and videos.
Some retail plazas even have other things progressives and democrats find offensive, like guns and old classic literature. Occasionally you can also find a pawn shop in a retail plaza.
There was a point where you would rent out your mall or retail space to anyone with the money to cover the cost plus a small profit. The decadence, wealth inequality, and unrealistic valuations from government interference have led to a world where it's fairly easy for some to cherry pick who they want renting from them based upon their ideological, political, or racial spectrum or beliefs. The same now occurs in our app stores.