You're right they don't make game streaming apps, but they very much get turnover from native games on the iOS store that xCloud would eat into. You can get PUBG, COD and the like on mobile that have IAPs that have to use the Apple payment system so they can take a 30% cut. Those sort of games are massive with over 100M installs on Android alone for just COD and I would imagine that both the install number and/or gross turnover of COD on iOS will be larger than that, considering Apple users buy more from the app store vs Android users from Google Play. There is literally no other logical reason why Apple won't allow game streaming services. Obviously Apple won't admit that's the case and they'll hide behind the guise that it's down to "user experience concerns".