I think Disney didn't expect it to be a problem.Honestly though, why hire Gunn in the first place if they're so concerned about people finding out about their director's past behaviour? It's not like Gunn made nice, wholesome family movies before.
Then suddenly it was a problem (or at least they perceived it could hurt their brand) and Disney has no loyalty to anyone but their shareholders so anyone who is a perceived to be a liability is not long for the Disney world.