In the article announcing the banning, Wizards suggested that it was willing to see if players would tolerate a "skill-testing, one-deck metagame." As such, it seems that a deck being 75% of the format doesn't automatically necessitate a banning
It also digs deep and fills up the bin which both help it to see a lot of play
Its spells cant generate value unless it has creatures in the graveyard, and there arent any effortless sacrifice outlets like Viscera Seer or Yahenni, Undying Partisan (which lack ETB effects)
Because she copies the spell you cast while shes attacking, a single [[Tainted Pact]] or even the riskier [[Demonic Consultation]] can get the job done
You can pull off a turn two win with a Mox, a Gitaxian Probe and a very lucky Consultation
Sometimes they are worth quite a little