First there are a couple of different issues. Deciding what’s on the App Store is one issue but payment processing is a potential separate issue.
Second 30% May have made sense once when this was a small business. It’s not anymore. Apple is inviting these lawsuits by simply not throwing big publishers a home with reduced rates.
Third, the whole tax on digital purchases is completely arbitrary. There was a time when Apple was working out what to do with Amazon and that’s when this role came about. Not being able to purchase kindle books just highlights the artificial and arbitrary nature of all this.
Fourth, at the risk of offending HN folks who self-servingly believe everyone wants or needs side-loading apps, most people benefit from the filtering of apps. Side-loading and unrestricted third party payments would simply be another attack vector.
Lastly, a bunch of different app stores is a terrible user experience. Just look at the friction of finding which streaming service has a particular movie or TV show.
I honestly think Apple could make most of these objections and potential problems go away by simply having a tiered percentage that rewards high volume publishers. It could scale down to 10% at which point the business case for an expensive legal challenge mostly disappears.