If a lot of companies would provide XMPP as a way to contact them, then what Google did would be as silly as taking email private.
Instead, most people are completely used to isolated messaging systems.
So I guss for Matrix, the challenge is to make sure that the dominant use of Matrix remains public. To some extent Matrix is ahead due to the bridging with large IRC networks.
But there are also quite a number of people trying to set up non-federated Matrix servers.
As a concerete example; imagine next month Google announces their own Matrix instance. All gmail users are automatically signed in. The instance works with other Matrix instances. A year after that, Google stops federating anything but bare text to other servers, claiming protocol limitations. They continue to make interaction worse for non-google users until the non-google users have no choice but to join google or loose their social network.
Now lots of people start using one particular Matrix instance for that kind of communication.
Now the popular instance stops federating and people can't reach the companies they want to talk to anymore.
The way Google took over was by offering a better user interface than other public XMPP services.
If Google is obviously worse than other Matrix instances, then people will quickly drop them.
Though XMPP had to deal with a number of paradigm shifts: images, markup, audio and video calls, persistant history, disconnected operation, security, threading, multi device operation. And I probably forgot a few.
Today messaging is much more established. So the matrix team has many more examples of features that are in common use and how other people designed user interfaces.
So it may be harder for Google to win through engineering. They may just break other matrix clients on android.