There are a few reasons for this
Jack is one of the strongest removal Characters as hes tough for opponents to remove and you reactivate his effect every turn
4 Eevee (Illustration Rare) $81.64 You Can Never Have Too Many Eevee This Eevee card is too cute to handle, with an adorable picture of a bunch of Eevee making themselves at home
The Cons Where this deck falls short is in the synergy between cards
When an opponent leads on a Swamp , you expect something disruptive, maybe a Thoughtseize , maybe a fast reanimation setup, but rarely something harmless
It has its own cardpool, MTG banlist, and tournaments, and in those tournaments mono black decks have recently started performing very well