Ahh I see.
Doing some research:
Only 30,000 average players online regularly.
Compared to 3 million average online Halo 3 players.
Roughly $60 mill made in sales of 1.74mill. ( Dev costs Were 60 mill at start of 2008, cant find final figure. ) The game likely hasnt made any profit yet. I would say antoher year onto 60 mill would see dev costs around 70-75 mill.
So with no profit and not much of an online community, I can see why they are halting DLC production. Doesn't look good for KZ3.