Firstly, I need to admit that I don't use Death much, but I think the reason it is not super popular is that its a splinter that you need to take time to figure out and most people do not take the time for it.

Death splinter to me is the debuff splinter, so you it takes time to find all the synergies and basically make your opponents feel dumb. I know I have felt that way many times against smart Death decks :D
!LOLZ