Well, it may in part be because they have a ready market. Their members and the communities in which they live might give them a boost that other small businesses perhaps don't have. There are business services and cooperative business services available now from the federations of cooperatives, so they perhaps have a better support network than other similarly sized small businesses that are not cooperatives.
As Mr. Harris was saying, it may be an area that is worth studying further. It has impressive statistics.