Well, my daughter did, although she looked like she was in the late stages of AIDS or cancer. She broke out. She weared nothing and her body type is sturdy, not stick skinny. They do it because it is highly addictive a nd feels good and they get addicted to it. My daughter did quit and I am rather awed and proud that she did.
The why is simple. The drugs make you feel good and your body craves it until you detox. And you have to be a strong person to stay off of it. It is a biological issue.
My daughter, clean now over ten years, tells me that the meth makes it impossible tos sleep so she used to take downers to let her sleep. She slept so much during the day. How did she quit? She wanted to. That is how and why people quit. Until then, they don't. It's very sad. I was scared to death.