Earlier quoted context omitted.
Why should they have to spend a month building a whole new iPhone-first onboarding flow and updating their entire app to accept a different subscription provider? Who's to say that if they spend that hundreds of thousands of dollars of developer time Apple won't just knock them down for some other imagined infraction?
Hundreds of thousands of dollars to create in app subscriptions? There are many indy developers that have done that as a one man operation.
Right now there's no mobile-first onboarding flow. That's a completely new thing they'll have to build. They'll also need to update all of their code that checks subscriptions, handles dunning, etc., to now work with multiple billing providers. So yeah, it's going to take a lot of time, which is a lot of dollars.