For a very simple fact, leaving makes us look guilty of something. Getting censored makes them look guilty.
They want us to leave so they can partition us off from the rest of the world and push only their narrative.
We have to stop retreating, we still have a beachhead on their turf, don’t give it up.
I agree that people who use those platforms should not stop, and that they want to push their narrative. But, I don't agree with your reasons - they assume the left has any ability to reason and logic. They don't.