I think Google showed with Windows Phone that they were very much willing to sacrifice a few users of their huge platforms in order to sabotage any competitor platforms entirely (e.g. refusing them access to the YouTube API, and refusing to develop a YT app for WP). I think that once Amazon and MS stopped developping their phone OSs, the message was well and truly sent: you either make a Google phone, or you try to make a popular phone without easy access to YouTube and GMail and Google Maps (obviously, Apple was already too big by the time Android really got going for Google to have any chance of hurting Apple more than themselves with this same strategy).