Same reason everyone else does it. Because I'ts intriguing and you wan't to "just try it out". For example with me, I wouldn't say that I'm a drug addict since I don't depend on it I just use it to have more fun or sometimes to relax a bit. Also He's the Ideal age for people to start experimenting with drugs. And also it just get SO much easier to get them when you're famous and so many people around you are using them as well