Several reasons. I actually know a TON about it. I am in the medical field. I have had more than my share of human physiology classes, anatomy classes, chemistry(my major in college, btw) and I know about the benefits. I have several friends and family members who ARE doctors, ect...... but I would rather not get them involved with my personal desire to be younger, healthier, BETTER. They would prolly give me some b.s. line about how I'm great, don't need it, am healthy, blah blah blah. It's my body. It should be up to me.
So, to answer your question: Because it's DAMN good for you. It makes you leaner, it's GREAT for your skin.... and basically, it's good for every cell in your body if used correctly.
That's why.
But my doc is an old granny-ninny. I hate her. Maybe I could trick her into giving me GH as she nears senility. Maybe not

A girl can dream, right?