There are really several reasons the pointy-haired managers don't "get" it. And it all falls under the heading,
We have a couple of managers in that situation right now, in fact.
Big IT has historically had 70% project failure rate anyway, which I've never understood. Just because a bunch of projects failed hasn't meant anything to these clowns, in the past.
Remember, this group of managers is such a nation-wide joke that they've been the main focus of the successful 'Dilbert' cartoon. Pretty much everyone *but* them knows they're a joke.
I worked for a company in the Dallas area for a year and a half on a comprehensive retail accounting project, when I realized after all that time that we hadn't shipped any product whatsoever. All that ever happened was meetings where the president changed criteria and requirements, and tried to act as though they hadn't changed.
In short, with moving targets so hard to hit, nothing got accomplished and my "survival alarm" was beeping like crazy. I left there to go to another position, and shortly thereafter the company folded. Stiff upper lip to the last.