In other slavic languages, words end with -k would become -cy when in plural. Take the word “peasant” for instance:
In polski, rólnik ->rólnicy.
In czeski, rolník->rolníci.
In Yugoslavic(Srpski, Hrvatski, Bosanski, Crnogorski), seljak->seljaci.
Perhaps this exists in old Russian and slowly disappeared since we know modern Russian don’t work like this.
Still we can notice this evolves, in castle age knights were saying “латницы”. But as imperial age comes, they say “латники” instead.
I felt weird at first too, but if putting other Slavic language in compare. This’ll make sense.