USBC has some dates that are already "blocked" for certain people. At least that is how I understand it. One guy in my area usually takes 20+ teams and has the same dates/times every year. So his are blocked for anyone else before registration even opens to the rest of us. He doesn't prepay these squads the way I do with my piddly 4+ teams, and if he can't fill all of them, he has until November 15th to let USBC know to release those slots.
At least that's what he claims, so it might be bullshit. It would however explain why the rest of us have to battle to get decent squad times.
I would bet that is the also case for some of the favored bowlers like Riggs etc.