Much of the value of any social networking site lies in the number of your friends who are on it. People flocked to LJ when all their friends got on it. With fewer people on it, its value to the remaining users is less.

A lot of people seem to use Facebook. I won't use FB except as a last resort. I'm leery of their repeated user-unfriendly policy revisions. I was hoping Google+ would fix a lot of the reasons I don't use FB, but it turns out that they have worse problems, as evidenced by their "Real names only" policy.

LJ has its problems but at least it's a known quantity.