I think they probably turn to drugs because since they have already everything they wanted, they might be looking for new experiences and new sensations, and drugs are exactly that.
I don't know what it is to have everything you want and everything you will ever need, but I think some people might get bored from it, so they might look at drugs as a way to bring a little more fun into their lives.
Exactly. Sometimes getting everything you ever wanted isnt a happily ever after life.