The point I want to make is that Messages is not preventing them from including Android users because they don't have an iPhone, which is a general misunderstanding that I often observe when talking with Android users who use Whatsapp or similar and is also recurring here. If the Android user gets locked out, it's because a human decided to, not because Messages refused to include that user based on ecosystem lock-in (unlike Whatsapp).
However, like Twitter OP, I can testify that teens attach a lot more weight to the blue/green than they should. But then again, it's everywhere in popular culture. Try finding a recent hit movie/TV series or music video, produced in the US, that shows green bubbles (or Android for that matter, even though it has a higher market share).
Have you looked at parental controls for carriers? Chats with green messages are in the log, chats with blue messages are not.
Depending how much they like their parents reading their messages, maybe teens aren’t attaching enough weight.
I imagine they get paid for using blue bubbles, just like other product placements.