It's the reason my friends and I all use Hangouts. Basically there are plenty of IM/chat options but Hangouts is the default app on about half of our phones (those who use Android). The ones who use iOS can still install Hangouts and we can all use it in our Gmail browser tabs at work.

It could've easily gone the other way. I definitely favor Android in daily use but if there was an official iMessage client for Android I'd have been fine installing that and letting the iOS users run their default.

But since Apple never did open that up we default to Hangouts. We could run some other app instead but at least this way some of us don't need to install "yet another IM client".