Facebook claims to have lost $10 billion due to a single iOS prompt giving users the option of blocking tracking. If side-loading were allowed on iOS, Facebook would have 10 billion reasons to push users to side-load their app, a pressure that doesn't exist at all on Android, which is tracking-happy.

Since Google lets most apps do what they want in most ways, there's not much motivation for bypassing the App Store--unless you're greedy like Epic. Since Apple restricts apps more with each passing year, the motivation is much higher, in addition to the identical 30% fees.