It's illegal tying[0]. Google used to force Chrome and Google Search as part of Google Play Store requirements. And were fined a few years ago by the EU[1]. Pretty much most of this reasoning could be applied to a messaging app too.
Why didn't Apple & iMessage run afoul of this same thing? Is it because Google was forcing third-party manufacturers to include things, but Apple of course just doesn't have that issue?
I've heard that since Android is the OS that 3rd parties use it could violate antitrust to include a Google branded chat-app. Apple does not distribute iOS so they can do whatever they want.
