Aside from conspiracy-theorizing about current events (and I don't use that term pejoratively), people tended to discuss the same topics. New cyberpunk media doesn't come out very often, so people tended to talk about the same books, movies, manga, anime, videogames, and fashion. Some of the alt-chans with dedicated cyberpunk boards would run out of ideas to talk about pretty quickly, since there weren't enough posts that the website had to prune old threads like 4chan did.

Another hypothesis I have is that cyberpunk media is not as captivating as it used to be since we arguably live in a cyberpunk world. In America there is unimaginable wealth inequality, with some cities having insane costs of rent for cramped apartments, with access to the best technology and medicine in the world but only if you can afford it. We also don't have to use media to imagine a world where digital corporations have a huge amount of power over daily life and the government spies on everyone all the time since both of those things are happening right now. I think we live in a cyberpunk world, it just doesn't have huge buildings, neon lights, and widespread punk fashion.

I came in contact with a few guys who wanted to make another alt-chan with a different model (see what other users are typing in real-time, and all posts get deleted early in the morning) but it never materialized as far as I can tell.

Edit: do any of you want to join an online cyberpunk community?