I think a death statistic would make player profiles look weird especially for players with high amounts of PK's because the death stat for them would be high and trying to fit a 6 digit death number beside a 6 digit PK number would be hard to properly fit and just look really weird.
Not to mention, there is a huge difference in losing a spar and being killed, spar is a one-on-one activity so the only thing attributing to the loss counter is a constant variable(as in, there is only ONE way to lose).
There are numerous ways someone can die, baddies, spar losses/ties, etc. Most notably would be when someone solo PK's a tower and ends up in 5vs1 situation, given all these factors there is no way that the number of deaths can ever accurately represent a PK'ers ability to PK. There may be ways to change it so things like baddy deaths don't count towards the statistic but that would just be a waste of time to implement.