Personally, I think it's primarily a collective action problem: people don't come here because there's not enough people here.
Regarding friction, the lack of algorithms could be cited as an example, but maybe the lack of quote boost is a better one. As I said earlier, I often don't boost because I can't quote, but instead make my own post. The original poster doesn't know their post engaged someone and that's a disincentive for more posts.