Something happened that no one could have possibly predicted. Metallica's collaborative effort with Lou Reed was a complete sales flop. "Lulu" sold 13,000 copies in its' first week of sales. This is compared to the poorly mastered "Death Magnetic" which sold over 500,000 in the first seven days.
I'm sure we will start hearing Lars blame internet music pirates and ninjas for the low sales as that is surely what happened here.