Microsoft tried that already. It failed miserably. I don't think they gave a reason but I suspect that garbage collection caused too many freezes in early 2000s hardware.
Yes, basically when Longhorn started to fail to meet expectations, there were two possible ways, do what Google did with Android, push forward no matter what to make it work, or forcing a rewrite into something else, which is what WinDev ended up doing.
macOS sandboxes apps, which are usually written in Swift or ObjC and thus use reference counting, and doesn’t suffer from the kind of slowness that plagues UWP. So your hypothesis appears to be incorrect
