It's always been something of a laptop thing? Microsoft since Windows 8 has made it somewhat clear they think Windows needs a strong presence on ARM tablets to A) avoid Intel hegemony, B) remain competitive with the iPad in that space. "It doesn't run any of my apps," was perhaps the biggest complaint about Windows 8 ARM tablets, so it makes sense that x86-on-ARM was a big strategy push before the next attempt.
Beyond that, rumor has it that Microsoft hopes selling tablets/laptops with ARM will open the Windows ARM space enough in the meantime while the Windows team is finishing the next version of key Windows shell components (nicknamed the "Composable Shell" or CShell), which would be make the Continuum experience for say Phones stronger because instead of switching entirely different shell applications (start menu, taskbar, et al) between form factors, the same applications responsively adapt themselves.