My bet would be that there's a double standard at work here. Scalzi is not little people, so he must be listened to even if they don't want to. Alyson Littlewood is not as well known or as male, so they can thumb their noses at her with impunity.

Alternative theory: they were OK with scalzi jumping ship when it was just scalzi, but now they fear a mass exodus of legitimate authors, leaving them with a nomination list of truly awful crap and nothing else. So they have changed tactics.