Because Stuart had a problem with crystal meth.

Sir, it hurts at first, but pain goes aw… But your dad's been doing a great job ho… Everything is so black and white. Oh, that's not true. We have to find Sam now. Did sue, Your Honor. Because the way we're living it is going… Only for guy talk. It's not easy for me to visit this town. Pop, couldn't you just sit there and eat… Fucking a vampire don't make you no expe… I'm eating. Well, I'll be right there, sitting in th… But there is someone. We have to stop him, Dean.