Apple famously didn't use it because it didn't sit inside their walled garden and they couldn't put any ads in it, take a cut of every sale, nor charge developers annually for the privilege of building on their property. That's 3 revenue sources that users and developers were skipping out on.

Android phones had Flash support and it worked well enough. Was it desktop-level, of course not. But Android native apps themselves were a mess from a power consumption standpoint until they implemented a JIT compiler in v2.3 "Gingerbread" as well as a task manager that freed up RAM by closing inactive applications. I remember specifically choosing an ASUS android tablet over an iPad because I wanted to use the full web, open multiple tabs at a time and play Flash games, rather than deal with iOS' "one app open at a time" philosophy.