In Europe it’s WhatsApp or Telegram all over. I have maybe four people I know I can reliably text on iMessage. This green vs blue bubble is rather an example of how self centered America is, always thinking its own big bubble is actually the world. In Tech that’s quite clear to see.
It's quite frustrating as it's a uniquely North American issue. I also never see this being fixed, as I'm fairly certain iMessage dominates in markets where the iPhone also holds a majority market share as well (makes sense). If you're an iPhone user in north america, many of your friends use iMessage so you don't care about this. If you're an iPhone use elsewhere, you still don't care as you most likely use whatsapp, telegram, line etc.