Because people are leaving the new 52, or because DC put out so few books in the 5th week of December is the big question. Time will tell!
Can I answer all of the above? I think the 5th week is a legitimate issue to raise, but I'm also sure that people are now starting to make realistic decisions about which books that will continue ongoing. Two other factors...people could be like me, and have started to move away from hard copies, to digital copies...no stat will ever really take that into account. Also, at some point, Marvel is going to stop double shipping their books right? It's getting a little crazy the number of their books that are being put on a 2 issues per month shipping schedule. I can't imagine them sustaining that schedule, and when they do, that might very well drop that market share right back down into DC's favor. I think the double shipping was a very reactionary move by Marvel, that began almost immediately after DC's announcement of the New 52, and seems very shortsighted. It just can't be a realistic long-term strategy, in my opinion.
I know I've left the new 52 for the most part.