They don't have to train that much, but they choose to. This is because, as Rip said, they are athletes. To get good at a highly technical skill (like the snatch and C&J) it takes a lot of practice. But to engage in better, higher level practices, they need to be stronger so they can practice their skills (the snatch and C&J) with heavier weights. And yeah, it is a lot of work for people working or studying on the side. That's why not many people do it. I am fortunate enough to coach two highly motivated and talented athletes who push each other.