Why does Coalgirls think there's a cartel?
There are definitely a few circles of friends in the fansubbing scene who work with each other a lot and tend to join each others' groups. "Cartel" would imply some kind of coordination between the groups themselves, though, which isn't really the case. It's more just that there are less people in fansubbing than you might think, and the especially productive ones tend to work for a lot of groups at once.