if ending with logy, why is necrology not study of death instead of list of dead??

Because, the word was not coined after (Classical) Greek had ceased to be spoken. Originally, -logia[/i] mean 'gathering together': e.g., anthologia meant 'bunch of flowers', before becoming a word for a collection of poems or other short texts. The suffix is related to the Greek verb λέγω (legō) 'to pick up, gather, collect' (link).

Ceci n'est pas un seing.