There's a lot of signs there for you that some people just don't care about you that much, or maybe you have all the wrong set of your online friends. On this site, there are some ways for you to tell if your friends are really your friends like they say.
#1 They never add you back, not even after a whole year or so, although they're on this site all the time. They just don't care about getting any new friend, that's all. Some people on this site never read their mail, others never add anyone back... It's not your fault, so don't take it so personal, okay?
#2 They're never around to comment...