I don't think this has something to do with social anxiety at all. It might have been true IRL, but once behind a screen, most people stop being asocial.
Well, I think this depends more on the site really. Some sites are just not really good for socializing and SH is kinda one of them.
Lurkers aside, some just don't have anything to say at all. But that's not necessarily a bad thing, as people tend to be more vocal about things they dislike rather than about things they like. In my story, I had the most comments on a controversial chapter, where people started to argue in the comment section lol.
And also seems to depend on the author I guess. I have encountered many, many authors that can't take any negative criticism. In the situation like the one in your story, another author would probably gang up against the one they don't agree with.
And yeah, if people all agree, then there is nothing more to discuss. It is these different perspectives that makes any discussion worth it. Too bad the other side of any discussion tends to be silenced.
Then, there is also the fact that comments tend to follow an exponential function. People are more likely to comment a chapter if they see there already are some comments while they might be more reluctant to do it if they see an empty comment section
And also depends on the site. The same thing can't be said for something like Facebook or Twitter for example where discussions are encouraged. In fact, and empty comment section is an encouragement for anyone to comment. But then again, this isn't like them . . . then again Youtube is able to do this stuff while sites like SH can't.
For me, it is more of the infrastructure and culture around here that kinda discourage discussion. SH kinda is a poor version of RR and RR already has issues with these kind of things. SH just makes them even worse.
In a way it might have been much better for authors in the long run. I don't think that most can handle reading any negative things about their stories. Silence is so much better than being hurt, I guess.
The rich get richer and the poor get poorer effect, I guess ^^'
And for getting in the trending section and writing in popular genres and encouraging your readers to discuss (or even argue) and other stuff. If you hit the jackpot and your story gets a lot of interactions, you better keep it alive.