I suspect the very horrible interviews at top-comp places exist in no small part to make it painful to switch between them, to reduce upward pressure on wages. I think it's version 2.0 of the earlier wage-fixing scheme they got busted for. That's why even a rigorous standardized examination isn't acceptable as a replacement for their painful interviews, even though spending all that time on whiteboard quiz interviews is expensive—the pain is much of the point.