Flash existed for Android. Ignoring the fact that it was slow, buggy, and power-hungry—the same arguments against it everywhere else—why didn't it thrive? Why couldn't it compete with the Google Play store, if it would have been such a keen competitor to the Apple App Store?

You're way too hung up on this idea that everyone loved Flash until Steve Jobs commanded them not to. My understanding was that it was pretty easy to create animations and rudimentary games in it, so, sure, maybe creators were pretty fond of it? Maybe even too easy, which is why we saw "look what I can do!" Flash websites in places where it was entirely unnecessary and unhelpful (restaurants were notorious for this). But end users never liked it. Or Java applets, for the record.