They seem to make a point of using one or two flops each year. I'm thinking back to the G-Girl and Lady in the Water cameos in 06, or Yensid and the Last Airbender last year. Heck, they even based an entire show around Hellboy 2, which was a box office disappointment.
Also, how many of the big movies this year had "recognizable" female leads you could build a costume from? If you want to break up the all male case, have to find female characters somewhere.