I usually look through Active Topics then move over to the specific Galleries. If someone asks for c&c or asks for feedback on something specific and I have an opinion or something relevant to offer, I'll comment. If the OP doesn't ask for c&c I will usually only comment if I have something positive to say or have a question. When I do comment, being an amateur, I can only comment on what I like or don't like about a shot. I don't really feel qualified to offer the kind of in depth comments that some people can about studio lighting, composition rules, posing, post processing etc.
I do agree with you OP that I am sometimes surprised at the praise for certain shots and am left to wonder whether it's the poster who attracts the positive response and not so much the content of the post itself...not that there's anything wrong with that! If someone is a steady contributor to the site offering feedback to others and helpful advice, then their threads deserves attention, IMO. It's a trade off. If someone pops in once in a while and posts something for feedback but never makes any contributions to other's threads then they'll probably get fewer responses.
In most cases, when something that I find ho-hum is getting a lot of praise, I chalk it up to beauty being in the eye of the beholder and my lack of time and experience with this hobby.
I also agree with those who commented on the time of day making a difference. I tend to post photos later in the evening and on weekends so sometimes they just drop to the bottom of the Active Topics page with no comments by the next day, especially in certain galleries. Then someone will come along and comment and suddenly there are multiple responses. Maybe bump your thread if you feel like it didn't get enough views.