The only reason for this is that Apple explicitly disallows apps from linking to or even mentioning subscription options that do not go through Apple's payment ecosystem and pay Apple's tax. Blaming the ensuing bad user experience on app developers is a case of "why are you hitting yourself?"
> As for the 30% fee, why shouldn’t they get a cut?
That 30% is, ultimately, coming from our pockets. Apple wants it because it prefers our money in their pockets. We, as the consumers, should fight back and demand it be lowered because we prefer our money in our own pockets. I don't understand why I should advocate that Apple should make apps more expensive and should take more of my money.