Windows’s achilles heel is arguably its chief benefit - legacy compatibility and being the de facto platform for applications.
Back when I had a Surface RT, I thought it was awfully neat, ARM-compiled versions of Office, IE, Windows 8.x bits ran well and it was fanless with fine battery life. (although I surely sound weird, I had a Windows Phone back then too and the syncing with IE on both was a nice feature) It’s just they were pushing the Store then and if you jailbroke it, ARM applications were rare.
Apple is a pro at architecture transitions and can steer the whole ship, MS can put Windows on ARM all they want but OEM’s will be reluctant since it’ll be a relatively big risk to sell a “Windows, buuut…” computer and the popular closed-source applications probably won’t bother with ARM for a while