Premiere is getting a much better rate with WSB and its huge audience than it would with WGST, which, despite a good daytime signal, is AM only and not a real factor.
Premiere makes most of its money from barter, not any fees a station might pay.
That's all certainly true. And then there's the little matter of contracts. I suspect WSB did not take the shows without written assurance that Premiere could not just pull them away at their whim. And the contracts probably include a right of first refusal.