I wouldn't let it get to you too much. I've posted a bunch of improvs on this site. Sometimes, I get a lot of posts/responses. Other times, none. I'm not sure why that is. I think of my own behavior towards others posts, and sometimes I just download and listen. Other times I feel inclined to say something. In the end it doesn't really matter. It actually is a very, very rare person who will generously respond to you and provide advice and praise and encouragement etc. I wouldn't expect much from the average joe browsing these sites. Try to find a few good friends with whom to discuss music and share creations...and rely on them. That's working well for me and I'm not finding myself wanting for encouragement/feeling like I've been sharing with others.
On another note, I liked your composition! For some reason it made me think of Tchaikovsky, I'm not sure why. I especially like the stuff near the end around 1:28 or so. Anyway very nice.