Disappointment at the publisher's house, no doubt. Digitalspy says:

Perhaps this means that interminable IKEA shopping list scene in the second book was written as a standalone piece, then shoehorned into the story because he thought it was so good. It also explains the first part of the second book, which had nothing to do with anything that came afterwards. But this doesn't mean someone else couldn't pump up the fragments into a fourth book. Lots of hacking and typing and additional exploits of a Crusading Magazine Writer and more anti-social monotonal remarks from Lisbeth, a scene where she beats up someone twice her size, lots of Secret Perversion of nasty powerful men, and there you go. Did I mention hacking? There has to be lots of hacking.

(Note: didn't read the third. Thought the first was great. Thought the second was a mess.)