I think one part that gets easily overlooked is that they not in-house, and that's a feature.

That means even when an in-house team has the same expertise, they have to adhere by in-house processes and hierarchy.

If a CEO signs off a consultant contract, they dont play in the same arena, and can often side-step the hurdles an internal team would face, without anyone internally getting too upset (compared to an internal team side-stepping processes).