May be a useless opinion coming from a British masters in a different social science field, but the head of our program was someone who would only co-author with students or former students. He also supervised my dissertation, as well as some of my friends'. He was notorious for not handing in paperwork for our projects to be authorized, forgetting to submit our references, and basically doing nothing when he was clearly paid to do a lot of things.
My friend recently got an email from him asking her to edit a significant portion of her thesis because he had submitted it to a journal without telling her and had received some additional requests from the editors. I suspect he does this fairly often - choose students to supervise who 1) will not fail even if left alone, and 2) work on his areas of interest. I deviated from his 'plans' for me because I rejected his suggested dissertation topics and went for my own in a qualitative method, but plenty of my friends were pulled into doing free work for him under the guise of doing their fieldwork. If he likes what you end up with, he'll stick his name on it and submit it for review, sometimes even without consulting you. This long and continuing list of publications under his name, btw, is one of the main reasons his position is in such a safehold in the college and department.