But why would you need to convince them? There's nothing wrong with using a free matrix.org account unless and until you do understand the benefits of using something else.
The good thing about having the federated protocol is that people can use different providers and change providers without destroying the network effects.
It's perfectly fine if most people end up using one of very few big providers as long as all providers support federation.
I think we have to make a distinction between personal communication and mass communication. The former is a question of privacy. The latter is a question of political freedoms.
Matrix is a great example where you need that one tech guy to create home server. Otherwise nobody of your friend group can use it as intended to.