I assume this is a sort of "pitty-roll" for RNG to increase drops. By the way it says, the most kills you get the higher chance for a loot bag to drop. This would be to give a better chance at a drop without making it a constant increase. Say there's a 2% chance to drop, after "x" number of kills, let's throw a random number and change "x" to 10, then for every 10 kills let's say it add's +2% more of a chance. I'm sure this gets reset after a certain point, or it's the "x'th" kill that has an increased chance and subsequent kills have the same chance but it builds back up the "x" amount of kills. But what Boidster said, prob a hard coded thing and I'm just taking an educated guess at it. I haven't investigated it at all.