Metro worked perfectly well on tablets. And every OS since W8 has actually kept some version of Metro (in the form of e.g. larger touch-targets), because having a single version of Windows UI for both touchscreen and mouse-and-keyboard computers, is what enabled the creation of the "2-in-1" or "convertible" touchscreen notebook, a design that basically every modern Windows notebook instantiates.

Liquid Glass also makes more sense on tablets. I think Apple is copying Microsoft because Apple is also moving toward full UI-level unification between their desktop mouse-and-keyboard UI and their mobile/tablet touchscreen UI. They've already done it for some apps (e.g. Notes.)