Players need some way to figure out what is killing them.

Please give players some means to figure out what is damaging them. If not a combat/death log then have an in game wiki. Something like PoEdb that lets you look up enemies to see what attacks they have, how much damage they deal, what damage type, etc. There is no excuse not to have a feature like this in a game like PoE.

would be nice to have some kind of report. trying to figure out the damage type based on the color of whatever explosion killed me isn't totally reliable.

I've read that the common excuse has been that "it's hard to make". So I'm not sure if the servers are just totally random or what's happening there.

I'm pretty sure the biggest reason this will never happen is because it would make numerous bugs very publicly obvious.