I see what you are saying; that Steve Bannon should have banned Wolff from the White House. I would think the Chief of Staff does that.
Bannon gave Wolff a WH pass and invited him in day after day. Why do you think Priebus was fired? It is likely that he approved.
Not everyone in the WH in the earlier days wanted Trump to succeed. Bannon was spreading the word that if he ran for POTUS, the Mercers would back him. Do the math.