I talked to a couple of people who acknowledged it was a difficult decision, but they said pretty much what I mentioned earlier.
They've been doing one in the late summer/early fall for several years, and any other possible date represented a big conflict. Plus, they have to coordinate getting building security (this was at the MS Office in Manhattan) on a Saturday, getting food delivered for lunch, so there are a large # of things that have to be taken into account.
(And I just realized you and others have put together SW Fox for years, so you obviously know about the coordination). The user group/community leaders who put these together are often doing so on a volunteer basis. I can understand where you're coming from, though I know these people personally and I can say I don't think they intended any disrespect - it's just a matter of only having so many options.