Relies heavily on countermagic If the deck's counters are disrupted, it can struggle to recover
While it's true that this opens you up to potential blowouts when they wipe the yard with cards like Bojuka Bog or Tormod's Crypt, remember that we're going to be drawing extra cards, too, and we'll be putting cards into the graveyard on most turns, meaning we can recover from a Bog (or Draugr Necromancer) fairly quickly
Then draw cards equal to the sacrificed creature's power
Have you ever wanted to have an army of pingers like Prodigal Sorcerer
The mana of the Cube is designed to make two-color manabases really strong, and this theme allows black to play especially well with white and red, which goes a long way towards making sure that black is represented in decks
Many decks wont need these to be viable