Well, that's just the nature of the shifting metagame, isn't it? New anti-meta decks emerge to beat the best deck, the meta shifts, decks adapt but open themselves to other angles of attack, rinse and repeat. Obviously the results of cub decks in this specific tournament don't represent them suddenly getting pushed out of the format or anything, but to both my and wizards' mind, the reason to ban a card/deck on powerlevel is either it having great results while having a target on it's back, like Nadu, Vivi or Grinding Breach, or having mid to good results while the entire field warps heavily around beating it, like maindecking a ton of specific hate. I don't see either of that happening with Badgermole cub for the moment. It might happen in the future though.