Why do adults try to keep up with teen trends.?

If they’re parents, they may decide to follow the trends to get a better perspective on what their child is going through at school, etc. I’m not quite sure what you mean by "follow the trends." Keeping up with (by listening to certain shows or music) the trends is a good idea for the parent of a teen, but if they actually wear the clothes, etc., IMHO that’s silly and inappropriate and probably quite embarassing for their child. You would be surprised, though, how many parents actually like some shows on MTV, VH1, and the current music. It’s when parents actually try to act like teenagers that there’s a problem. Is this what you meant?

Zac Efron and Emma Roberts - TEEN Magazine Cover Shoot