Sorry, I need to side with Moish on this one.
#1: After a person is niftar (lo alaynu) there is a din v’cheshbon. We are sad because this is a tremdously difficult time for the nishoma.
#2: When a tzaddik dies, we cry that the earth we are on has lost a piece of kedusha. We also cry because we will no longer have access to this tzaddik. Rabbonim still cried after R’ Shach passed away, simply because he was no longer with us (for those who did not know, R’ Shach was not “functioning” at the end of his life).
King Shlomo even writes that there is a time to cry