Imagine you're a VP, or even a C-Suite Executive...
Your employees get to make decisions based on what they think is best, what feels right. You don't have that luxury. Investors, the board, other managers who are vying for your position all demand numbers-based decision making and justification. So what do you do? You hire a well known consultancy to produce documents and data that supports your position. You can now justify your actions by pointing to what they've made for you. And, you have the added bonus of the sunken cost fallacy. "Well of course we took their advice, don't you know how much we paid for it?"
So the VP's job is to be disingenuous to everyone except the consultants? He's already made up his mind about what to do, knows he can't get buy-in from employees, so he hires an external firm to generate the data he has already decided is correct.
I feel like all the comments talking about a breakdown of trust seem even more poignant now after reading your comment.
Your employees get to make decisions based on what they think is best, what feels right. You don't have that luxury. Investors, the board, other managers who are vying for your position all demand numbers-based decision making and justification. So what do you do? You hire a well known consultancy to produce documents and data that supports your position. You can now justify your actions by pointing to what they've made for you. And, you have the added bonus of the sunken cost fallacy. "Well of course we took their advice, don't you know how much we paid for it?"