The crazy thing is they did that for a while with the Wii virtual console, and I think they also had a Wii U Virtual Console and a 3DS one as well. The problem is the titles never transferred over, so you had to keep buying them over and over (though this is still preferable to the current NES/SNES/GBC Virtual Consoles in the NSO subscription). One of the things I think Microsoft actually does well is their Backwards Compatibility. If you buy an old game on from an old console, it'll still carry over (though my understanding is this is only possible due to having a PC-like architecture across all their consoles, so it's easier to achieve)