This has at least some to do with it. I've heard Hugh Arthur make the statement that he doesn't like having more than a couple of dogs that belong to the same person.There are several folk who have dogs with multiple pros rather than having them all on the same truck. I can only speculate as to the reason they do it. If I had numerous dogs (8 or more) and wanted and could afford a pro to train them, I'd split my dogs.
I would think that this would be a major consideration. If you have all your dogs with one Pro then you are competing with yourself essentially. By placing your dogs with different Pros that run different circuits, then the likelihood of competing with yourself is mitigated.If they are with different pros, running different trials, at least they aren't fighting themselves for placements.