You could say that about any obsessive-compulsive behavior. Why do gambling addicts go into casinos or spend their entire paycheck on lottery tickets? Why do some people repeatedly engage in high-risk sexual behavior or make hundreds of telephone calls in a day? Couldn't they 'choose to' do otherwise, or to stop their problematic activity?

Well, no they can't. If you're in the grip of compulsion you can dislike what you're doing, know it's a terrible idea, be fully aware of the negative consequences, but nonetheless be unable to help yourself, in the same way that it's hard for a passenger in a car to exert much control over a dangerous driver. If volition were such a reliable mechanistic thing then we'd have little need for psychiatric hospitals - psychiatrists could just tell mentally ill people what they were doing wrong and call them cured.