It's dowman sayman doing murder. Unironically go somewhere else if that's not your cup of tea, the person loves to be morbid in depressing settings, and this seems like a very depressing one.
I had assumed it's cuz they are reincarnators
but the adventurers apparently died permanently too? and at least some of those also reincarnated
maybe it's just a special ability for dungeon staff. since it's apparently so rare for someone to become one, if they died for good you'd never have any staff