It's not that simple though, even with the tools Apple provide to first help port your game to an Apple ecosystem and then between the devices it's much more involved than that. Each device has its own design considerations that has to be taken into account, for example just porting a PC version of a game might work ok for the Mac but its going to be an awful experience on a iPhone or iPad.
The amount of development time needed to make it a flawless experience on each device plays a big part in game studios deciding if its worth their effort and when the AppleTV has such a small user base it makes it much less likely that they deem it not to be even if it might need less work than say on iOS.
And as we have seen RE:7 has been a massive flop on iOS/iPadOS and that has a much bigger user base. And seeing as a AppleTV device that has an M chip and enough storage to make it viable as a gaming system is going to jack up the price and limit its reach. They would need to first do what most console manufacturers do but Apple has never been willing to do and thats subsidise the hardware costs with the aim to make it back elsewhere (they won't even cut the AppleTV price to get it more competitive price wise with Amazon, Google or Roku) and sign a significant amount of exclusives with a built in pedigree to the platform
Surely we can't say things like that until we know why RE:7 failed?
The impression I get is that the failure was not *technical* (ie it's not like people were either saying "this game crashes all the time" or "this game is so laggy and stuttery it's no fun"); the impression I have been given is that the problems were in the business model, ie, for better or worse, the targeted Apple consumers were unwilling to pay the price demanded.
If so, various very different options suggest themselves.
For example
- people though that price was unreasonable because the game was "old" and, like a movie in a theater, part of the price is justified by newness. Solution is charge same price, but release at same time as PC/console?
- mobile audience is never going to pay that sort of price (but is much larger). Solution is charge quarter of the price to 4x as many sales?
- don't sell as one-time product at a high price, sell as a subscription (or part of a subscription)?
I don't see much value in your argument of Apple selling a console via a console business model. Games are just not a great business to be in.
Apple's willing to to a little to help game vendors (APIs, kick-ass hardware, Apple Arcade, etc), but it's the vendor's job to figure out their business model. It's not Apple's job to build a competitor to X-Box or Playstation, I just don't see how that furthers any important Apple strategy.