I suspect it’s because App Store games are a totally different type of streaming service than apps like that just deliver subscription content like periodicals, book purchases or downloads, or a streaming TV or movie service where end users just watch, listen to, or read whatever content they choose. There are usually no other, or fewer, in-app sales opportunities other than for the subscription itself. Usually there are fewer tracking or ad sales opportunities than cloud based gaming offers. I think these are biggest reasons why Google, Microsoft, and other gaming services have their nickers in a twist.
I also think the new rule will enable Apple to more easily review every app that is locked up within a service. It also creates an option for people who just want to play one or just a few games rather than shell out bigger bucks for the full service with many games they will never want to play.