I assume you believe it to be left orchestrated. My guess? The overwhelming majority of young people (and people overall, though not by nearly the same margin) are left leaning or very left. It's probably just a demographics thing.
for some reason that phenomena only manifests itself on heavily moderated platforms.
on unmoderated (chans) or barely moderated (youtube) platforms, you get a much more diversity of thought.
I don't think people like to talk too much about why they leave online hangouts, because it's like admitting defeat, because people still at the place won't sympathize with you because they either disagree with your criticisms or think you're slandering the place (or else they'd have already left too), and because outsiders who agree with your criticisms of the place may have other criticisms of the place and judge you for being associated with or expecting differently of the place.
Assuming this phrase is about biases about race, then this is a dumb comparison. Biases about race and minorities are different than biases about political positions and opinions. Political positions aren't a protected class.
Also, if it is about a board usually called "TD" that one is quarantined, not banned.