Indeed if people post to a forum, one would think they would be expecting a response of some sort. The question is how do we respond?
If I see an really good photo, but it already has several "great" comments, then I'm unlikely to comment further, because I have nothing new to say about the photo in question. But the opposite problem often occurs. A number of people have said "great photo" and yet the photo has obvious problems, defects, etc. If I then critique the photo, people often get upset since they've been built up with all the "great" comments. Personally, I feel like we'd be better off with these types of photos to say "great, but ...".
If I see a really bad photo, then I usually skip past it. By "really bad", I mean the photo has no redeeming qualities. The photographer hasn't a clue what they are doing (or just didn't care and posted anything that happened to show up on their desktop), and so probably most comments will just start a war. I see a lot of photos like this. If I do comment with a long list of problems, then more often than not, an attack ensues, and that is not what I want to participate in. It doesn't take many of these attacks before you are reluctant to comment on the really bad stuff.
I do think the Main forum is overused for posting photos where comments are really wanted. Those should go in the various critique forums.
Oh well, I guess that the "several" I promised, so, "so long".
cheers,
rfs