Just my opinion, but FWIW ...
I believe many folks do not post, except on isolated instances, for a couple of reasons. First, so many posts get sidetracked from the OP's question/comment that the post becomes unrecognizable to its original intent. There's always a certain amount of drifting on almost all posts, but recently (the past year or so) they seem to drift further and further into very loosely-related or non-related tangents.
Second, and the primary reason I don't post a lot, is no matter what you say, there's always someone who can't wait to tell you how stupid you are for saying whatever you said or whatever you asked. Polite disagreement is an endangered species. There's absolutely nothing wrong with a person disagreeing with you or having a different opinion. It's the manner in which they express it. A person with a different opinion than mine is welcome to tell me all day why - just do it with a little bit of courtesy and offer some reasonable suggestions for improvement. An intelligent and courteous defense of their position opposite mine is a strong tool to possibly make me reconsider my position. Maybe I'll change my opinion, maybe I won't. But I will listen.
However when you have nothing to say but "You're an idiot for thinking that way", "Maybe that works at the fifth grade level, but ...", "Maybe writing isn't your best option in life", "You need to throw this crap away and trying something different" etc. Why not simply say, "Well, I've found a few issues here that are important. Here are the problems I noticed and I have a few suggestions that might help" - then offer those suggestions without first demeaning the person. Also, I give little attention to those who are rude, can't wait to criticize others but refuse to post any of their own work for review..
I've spoken with three other members here in private, and they all feel very similar about it. It's not a matter of thin skin or not being open to criticism. It's matter of simple courtesy and respect for your fellow writers.