Because, Microsoft and even linux have hardware abstractions that mostly conform to a spec. The spec in Android is complete crap and largely ignored by the hardware vendors. In Windows and linux you get the complete OS from the OS owner (MS, or ubuntu or red hat etc...) and each driver has to match the spec exactly or the driver will fail, with Android you are getting custom forks of the OS. Each one is customized to the hardware and has a different behavior.

In short it's MUCH easier to support different hardware in the PC world because the OS vendors have standardized the specs and in Android it's very wild west, each hardware vendor is supplying their own version of Android which is mostly the same but has subtle but key differences.