They make billions from that 30% cut, and the only reason they can do that is because they disallow all other payments, or even a mention in your app that you can pay elsewhere. They would never be able to charge that much if they allowed any competition, which is exactly why they need to be regulated to allow it.

They can't charge a cut of revenue unless they monopolize payment processing, so if as you say they start charging for developer tools, if they charge too much of a flat rate for those, many developers will rightfully walk away, so no, they can't make obscene profits like they're doing now without controlling all payments in iOS apps.