It's a lot easier and cheaper to switch from a $10 a month Netflix subscription to a $10 a month Hulu/HBO Go/Amazon Prime subscription than it is to switch from an iPhone to an Android phone.
Those all have different programming. It's even easier for loads of people to scream at Apple for removing one of their favorite apps.
The big players can dictate a lot of the rules of the game.
They also often get their own rules. I've designed apps that onboard exactly like the big boys, and been rejected.
Sometimes. Apple certainly pushed back against Uber when they were skirting the rules a few years ago.