Zazen, the score is designed to follow the "way of fight" of the majority of the players. That is, if 90% of players play for K/D, then K/D will be a mandatory factor for scoring, if next month 90% of the players play for K/H, then this will be the mandatory factor, and so on. Of course, most players play just to have some kills as soon as possible, surviving doesnt matter, so K/H is mandatory while K/D is secondary.
Independently of working for K/D, long range missions (sweeps, caps, buff interception or whatever) imply a lot of time, and not all the times you get more than a single kill. Actual scoring system punishes that kind of missions, while these are just the most reallistic ones.