Like most other gaming terms, this one comes from other games where the environment's a little different. In many games, you can position your character to defeat endless supplies of enemies (or any particular action) for the purpose of specifically raking in some sort of reward. The name has just carried over here, even though when you defeat an enemy here, you have only a small percentage chance of getting that reward.
Game terms are pretty resilient. I wouldn't hold out hopes of changing a term just because it fits better here.