1) I think someone must be very bored to do something like that. I think it is a foolish thing and very dangerous. In any case I don’t think we can generalize about the teenagers because I am pretty sure enormous part of them will never think about doing it.
2) Maybe because teens ages are rebelion ages and everybody did crazy things on theirs teens. It is a stege where you are discovering new things.
3) There are lots of things to do instead lift-surfing. Maybe play sports or go to excursions where you are not putting your life in risk
4) 5) Nowadays teenagers in my country are playing videogames or surfing on the net. But when I was teenagers I remember we were much more on the street, playing and runing. I guess things are changing.