In many respects iMessages should be considered a stand alone app like WhatsApp since people need to be in that particular app or it doesn’t work. The fact that Apple combined SMS and iMessages blurs the line and while awesome for iOS users it’s caused this issue for itself while people now expect group chats to ‘just work’…
Sure, it’s a marketing piece to help drive people to just get an iPhone so they don’t have these issues.
Conversely, and the harder thing, somehow convince all their friends to move to some other platform… No wonder that people fall back to Facebook Messenger. Facebook seem to have gotten smart enough to allow people on messenger without having Facebook (as I understand it).
Apple and Google would do well to work on a standard messaging protocol they could both use to avoid the likes of Facebook stealing that function, but I just don’t see that happening.