I imagine not only is this a technical challenge in general, but the "best" apps require google integration and google is giving devs and big companies incentives to require the google play libraries, which this can't use. This has been google's main dirty trick since the beginning, which is why you don't see much competition in the android space. Its a few big licensed players. Niche, homebrew, emulated, etc players aren't going to get google certified. Android has just become MS from the 90s. Google is a crony capitalist tough guy as much as MS or Oracle or Apple, it just has better PR as being "friendly" and "open."

MS also is clearly bribing/paying for big apps to come to its Windows platform via the Windows store, so why bother with this Android middle-man that is all trouble? Eventually the big apps got to Windows Store and that's really all that matters to 90% of customers.

Everything about this project was doomed from the start. I think MS just has given up on apps and mobile and leaves that to Apple or Samsung, who are now just caretakers for ios and android at this point and mobile becoming a low/no profit commodity in the long run, outside of payment processing.