Apple Arcade explicitly forbids
any in-purchases or ads. So not sure if we can compare a subscription service to a marketplace like App Store.
In Arcade of course Apple is paying money now to get enough content on the platform to make subscribers come, same MS did with Windows phone etc. Market place always need boosting either on supply or demand side to get started, it is unlikely Apple or anyone else starting a market place will continue to pay once the market is large enough.
Xbox/ PS keep paying since they know that marquee games are reason many times one the console is bought. For android and iOS market to be considered as one market there should be that level of competition at least.
While streaming has reduced privacy to large extent, the streaming business model whether subscription or micro-purchases (rent/ buy or song / album etc) have been always a threat to studios. Everyone is rushing to do original content yes , Netflix, Prime and Apple are already able to produce similar quantity and quality to studio in new content or will soon enough, however streaming companies cannot compete with the back catalogue for next 20-30 years.
Disney+ and is pulling out of other streaming services today. 5 years from now, Netflix may be ready to multiples than they were paying, just for non exclusive access to that back catalogue of Disney.
Disney will not care whether Prime or Netflix is also showing older disney back catalogues as long they have enough people paying for disney+ , where newer and some exclusive content is available. Their ownership of Disney+ means they can always negotiate from a position of strength. Studios are distribution companies first, content producers second. If you control distribution you control the price.
While the studios are taking the ball home today, I am not sure they will not be back later . I am not saying any of this why Apple is why they charge differently for streaming, just that the industry is in flux currently.
P.S. Had Jobs been alive, things would have turned out differently, I think Apple would have likely acquired Disney, it is a good fit, Jobs owned substantial stake in both.