"E pur si muove!":
It may not be so bad, from their point of view, if their interests coincidentally overlap with theirs, as long as their interests and concerns don't come from you. As a result, though Teenagers can be interested in the same things that their parents are interested in, it will often be as if they weren't.
Second, many teenagers live under the thumb of inscrutable, irresponsible authority. 'Because I said so!' 'As long as you live in my house you follow my rules!' They are in a state of rebellion because, unlike you and me, they have plenty to rebel against. Most families are run like little dictatorships, with authority exercised either by arbitrary fiat or 'rules' made by a power that answers to no one. For a lot of teenagers, it would show a lack of self-respect if they were not in a state of rebellion.