It works the other way around too: consultants make very convenient scapegoats, which allow managers and executives to push for change (via the consultants they hire) without risking their own neck.
This thread of thoughts is the reality I have seen first hand.
Management consultants are simply there for often political reasons. Sometimes as an extra pair of hands, but often not.
In addition to the reasons given, it was also sometimes as simple as inept ivory tower management having lost faith in group and deciding they needed to hire real pros to come in and fix things. Another one: Management never wants to point the finger at themselves. They hire some real pros to come in and lay down what went wrong. I hated that job--swimming in bullshit all day every day.
I have so many ridiculous stories I've experienced in my short time doing that kind of work that I don't think the average person would believe.
Want to do something, but you know the public will riot if you propose it? Hire some big name consultancy to write a report that basically deliver the same message, but now with an air of clinical objectivity...
