There’s been dozens upon dozens of posts and multiple threads about this sort of thing, yes, Sonos has considered it, and it isn’t apparently easy to do. 

I think the fact that there are so many androids make it really hard 

I’d agree. It’s been discussed at length in multiple threads, over the last several years, with that being the most frequent comment. 

The idea of an external mike is that it would eliminate the various Android device microphones. Sonos would only need to provide a single mike profile that would work on all Androids.

Actually it might be designed to work on Apple gear too, then Apple devices would be usable the day they are released. No custom tuning for each model and revision.

Again, discussed at length in many, many threads.