Apparently kids in the 10-18 range think that smoking to the point where you're seriously fucked up and drinking till you're passed out, is "cool".
It's popular. Everyone does it. It gives you "status". It makes you look "cool". It makes you feel better than someone else who is clean. It is perceived as THE thing to do in order to gain popularity and "coolness". And we all know how much of a "I'm better than you" show it is in high school.
Personally, I'm clean. I have my own natural high. Ask anyone who knows me. If I'm not laughing, I would have a huge smile on my face. I've drank before and done the "weed" thing and it actually made me feel like shit. You can argue that I have only done each of those once and I'm not fully used to the feeling yet but when I have my own natural high, I really could care less.
Plus, in a selfish way, if all those dumbass social-elite wannabe dumbasses screw themselves over, then we would be wayyyy better off without them.