Large firms will have seen similar changes and similar problems, so they tend to know how to frame the question, how to ask the question and how to surface the situation. I think the government is going to large global firms because they've done it before.
It goes back to the value proposition between public servants and consultants. When the consultant has done it 50 times before, it's going to be a lot faster for them, versus time for the public service to even develop the questions.