With Twitter you have to remember that a lot of people re-tweet messages without seeing them, there are sites that can be set up to re-tweet messages from those you follow that look for a particular hashtag. So just because someone is re-tweeting your tweets doesn't mean they like or have seen your work.
On Facebook a lot of people like someones elses work in the hope for a like back, or they may belong to a group and feel duty bound to like a few images everyday because they are receiving likes on their own work
Personally I wouldn't bother to much, just enjoy the fact that your images are traveling around the world so easily, something that wouldn't have happened 20 or so years ago :)
