Why do kill rights expire?

[Ibex_Horrne]

@Buggs_LeRoach

zkill shows you’re mistaken . in fact they were ganking in the same system the next day , and active all month .
if it takes you longer than a month to get your courage up , let it go , or sell the kr as some suggest .

I added them to my contacts so I would have heads up as to when they were on. I never saw them on everytime I logged in which was at least once a day. If zkill says different then I don’t know.