Good for you, and all other Messenger-only-users. But why force all other users who are using the Facebook-app to open up a separate app when they want to send or read messages?
They also didn't want to split the user experience of using Facebook messenger on mobile and hence the forced switch.
It was only a big deal because of the surface area of the world that the main Facebook product (w/ messenger) covers. I guarantee you that if Google did something like that no one would care (at least not enough to give 20,000+ 1 star reviews)
This reminds me of the talk "Is it really Complex? Or did we just make it Complicated?" by Alan Kay.
The complexity of the underlying problem, messaging, has not changed, but FB has made it a lot more complicated.