In order to convince people to migrate, you'll have to do more than just build something better.
There are many tools that people are stuck using, even though there are better alternatives out there.
And yet, these better alternatives remain the no. 2s or no. 3s in their category. Maybe lower. There are multiple reasons for people's hesitancy to migrate. Four of them are:
Network effects
The hassle of migration
Ignorance
Having to admit they made the wrong decision
The network effect pulls people back into social and messaging platforms. This of course is nothing new, but think about it this way: if you were to create an alternative social platform with more regard to privacy and ethics, how could you possibly break the strong network effect of an existing company? To understand this, you have to understand how people adopt new tools: people want what's new, not what's better.
Certainly the better tools will attract certain kinds of people. But these are the people who were already convinced they needed something different, and were probably looking for it. How do you reach the rest of them? By creating something new. Something they haven't seen before.
Now, it's very much possible that the no. 2s and no. 3s are comfortable being where they are. Maybe they don't want to convince most people who use their competitor's tool. And maybe they just want to stay focused on serving a specific kind of people. That's completely fine (and quite necessary at first).
However, many companies that are set to bring change to the world, do the same thing over and over: they try to become like their competitor. Instead of innovating, they are copying. This way they'll always be one step behind the competitor. They even position themselves as "just like the competitor, but better at certain aspects". They don't say this explicitly, but it's implied in how they position themselves.
What "better" companies should do instead is to create their own path. To cause disruption through originality. The dominating companies have already made a name for themselves in their category, and people don't like to admit that their original decision was wrong. By telling them that they should migrate, you're asking them to admit this. But if you create something different, something in its own category, your solution is just a new kind of product they're trying out. It's an experiment, not a leap into disloyalty.
Don't be the alternative. Change the game.