My reason would be...simply put...Ive ALWAYS had an interest in training, exercising, nutrition, and generally anything that can make your body faster, stronger, healthier, and more able. In becoming a PT i get to learn everything about the body's mechanics and functions that allow it to be such an incredibly well-oiled machine. If being a personal trainer made more money and was more prestigious I'd probably do that...but it doesn't make money, isn't prestigious, and doesn't give ANYWHERE enough knowledge to really help people medically.
People ask me why I wanted PT over MD or PA, somehow assuming they are even slightly related. I wanted to be a PT because of the things I mentioned before. I have no interest in testing people's blood, giving shots, looking in people's eyes, nose, throats, I have no interest in sewing up wounds, cleaning up infections, or prescribing medications. My one real interest is in making people stronger, faster, and more flexible by teaching them how to exercise and give them a chance to better their own health through teaching - something medicine really doesn't accomplish.