Yeah I can't understand why people think that inviting new middlemen into their transactions is acceptable. It's time to stop prostrating ourselves to these companies.
Same reason people use credit cards or Gmail or hell Patreon. It reduces the number of counterparties you have to deal with and trust.
Facilitation of transactions and assuming the risk.
It's worth it to many. I gladly pay Apple the extra 30% or whatever because it adds up to <$10 per month for me and I don't have to jump through hoops to cancel subs.
Apple has given me a simple way to manage many of my subscriptions, a single pane of glass, which I appreciate. I'm fine paying a little extra for that.
It would be more valuable to me if Apple didn't charge too much, which turns away service providers.