In my brief tangles with the industry, I noticed that it was common for an agency to have a few A listers, then lots of B listers. The model was that the A listers would pay the bills, and it was worth lavishing time and attention on them. The B listers would be effectively put in a holding pattern with just enough effort spent on them that they didn't go anywhere else, on the off chance they eventually became A listers. The B listers could say that they were represented by a firm with real legal clout, and the agency could inflate the number of actors they were representing, but other than that the benefits seemed to be pretty intangible for the B listers.