I don't think anybody is looking at his numbers and says "Oh, my k/h is only x.xx, I quit!".
People quit because of not having enough fun, which can have various reasons of which 'not enough action' may be one of the more important ones. (And yes, players also quit for financial reasons or lack of time or old age, but that's not within the scope of this thread)
Although it's interesting how low the median is. That says to me there were relatively few people pulling the average up with large numbers of kills.
But it's interesting to see that the ratio of (AVG/MED) has become smaller over the years, which is indicative of a more homogenous population than ever before (many older players, few newcomers).