The overview in the spec is probably as good of a summary as anyone could give you.

But some of the comments for that video suggest that they aren’t able to connect to people outside of that bubble, since these people’s instances might block NSFW ones.

I think a lot of times that’s due to the risk of hosting potentially illegal federated content from nsfw instances.

4chan definitely got worse. like it was always edgy and stupid, but after 2015 every board just kind of became /pol/