Microsoft lost (not missed) mobile because the Windows team had been losing the ability to execute competently. iOS was essentially macOS for mobile, and Windows wasn't competitive with macOS on the desktop and still isn't today so it wasn't a big surprise that they couldn't pull off great results on mobile either. For as long as the mobile playing field didn't have the most competent companies doing software they could be the leader but once Apple/Google showed up the piles of tech debt and general apathy got the better of them.