And they left because they were done with their respective projects, and maybe because of negative comments.

Eliezer had said the things he was planning to say with the sequences and had found new research fellows to start working on AI again.

Yvain was a sock puppet that Scott used on a role playing forum he was active on and did some LW posts as backstopping. Then he continued posting here for a while but writing without politics and not under his own name felt too much like hard work. Now his entire blog is pseudonymous because writing about politics under your own name is not such a good idea, but it is still all about political conversations rather than the sciency stuff he did as Yvain.

But it was not about Eugine or downvotes because they always got much more upvotes than downvotes on damn near every comment and every post.

And vice versa.

Yep. It's a negative feedback loop, there's a reason it's known as the death spiral.