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The Surface I think was mostly there to demonstrate that you could make a not shit looking Windows laptop and try to nudge the main manufacturers to up their game. I don't imagine they've actually made anything particularly significant from the hardware itself.
Far more lucrative to get people onto Xbox Game Pass subscriptions and cloud gaming. Let Apple/Intel/AMD/Nvidia worry about the hardware and just make sure that their stuff runs well on all of it.
Microsoft are more interested in XCloud than on mobile hardware. They would prefer to have xbox games work well on iPads / android devices etc as well as Apple TV and smart TVs than make their own piece of mobile hardware.