I think a couple parts of the equation are:
Score streaks are easier to get particularly in objective game modes (kc included)
Streaks are not linked to classes. In mw3 if the enemy team was doing well and people weren't getting their high streaks they could change classes to more attainable/ defensive streaks.
Lastly and its going to sound silly but SAM turrets would really make a difference in this game. Simply because people are too lazy/selfish to shoot **** down. I used thousands of SAMs in mw3.. I think it would help more than it would hurt.