Friend Issues

I've gotten to a point where, if I step back and look at all my friends, only about two of the six actually seem to care. They give and take an equal amount of time in our friendship, despite the distance, and that's so important to me. But, how can I just let go of the others? I don't want to, they're important to me, I've put so much effort into our relationship, but they don't seem to care anymore. They don't reach out, they shut me down when I try to make plans because they're always busy, they expect me to do all the work of they do decide to hang out, they only call to rant about their issues, never asking how I am... It just sucks because you can't make someone care, no matter how much you do.