Maybe it's because the people on the forum don't recognize you or what you're posting doesn't seem to be interesting to them.
I had a hard time getting started here on BYC, but when I started commenting on other people's pictures, I started getting comments as well. If you want others to comment on your pictures you need to post pictures that others are interested in. Usually when I post pictures it's because the content of the picture is special to me, but it might not be for others, therefore the reason for no comments. I have no intention for this post to be offensive, but rather helpful.
Take note of the pictures that others comment about and practice posting to see what seems to get attention from others. Often the pictures that get my attention are the ones that others don't seem to find interesting, so I have learned to take pictures in a way that others seem to like and readily comment on. Sometimes I'll just post a picture for the pleasure of others and don't expect to get any comments.
Happy posting and learning!