My dad had four sons (technically five; one died shortly after birth) who are my half-brothers. When they were young, their mother basically abandoned them and hooked up with another guy, who she eventually married. So, my dad had to raise three babies by himself for five years. Eventually, they moved away to live with their mother in another state. He later remarried and had me. One came back, but the other two stayed in different states. They never showed any interest in having a relationship with my dad, and I know it bothered him. For some reason, they blamed him even though he wasn't the one who left them.
Well, their mother eventually came back to live in the same town we do. When her husband was dying, the guy she left my father for, one of my brothers came down to see him (his stepfather). He briefly reconnected with our father, and while it went well, he never bothered to stay in touch. When our father died, he didn't even come to the funeral. Neither did my other brother, though he is basically homeless by choice. So, I can sort of understand that, and at least he expressed sadness about it. I'm trying to not hold any resentment toward my brother for that since it's not the Christian thing to do. However, I deleted him from my Facebook, not that he probably cares anyway. I'm not going to bother trying to have a relationship with someone who obviously is not interested in having a relationship with me or my father. All that is to say that I can understand how you must feel.
In your case, I suppose it's only natural for adolescents\young adults to drift away from their parents as they establish their own identity, independence, and build a life for themselves. Then later in life, when they have their own families, to grow back closer to their parents. Maybe this will be true for you and you just need to give them time and space to grow. The other alternative is you could talk or write to them and express your feelings about it. Maybe they will understand or maybe they won't given their limited life experience. But I think most people come to appreciate their parents the older they get (assuming they had good parents). Hopefully, yours will come around too.