Some places call back WAY more people than they're interested in.
The rumor this year is that some places are calling people back but have already decided on rejections before you even walk in the door. The idea is to drum up interest, get people telling other students how nice their callback was, get people to reapply after doing clerkships, etc.
At least for one of my callbacks I'm pretty sure that's what they're doing. My grades make me woefully unqualified but they know I really want to wind up in their city.
The other CB is from a place that's doing so horribly I don't even know why they're hiring, and last year gave out 1 offer for every 5 callbacks they offered.
Given the state of public interest hiring right now I think it's fair to say at this point that my situation is hopeless.