I've seen a few big threads talking about Lemmy (because people posted links to them here, on Lemmy to explain how this whole thing works and get people on board), but at the same time I've also seen people here posting their experiences with such discussions being removed.

I would have to suspect the admins aren't doing anything, but the individual mods of some ass-kissing subreddits do so because they feel threatened on behalf of the company they volunteer to prop up.