Hire you for advice and then don't listen to it

I had a situation where we were hired by an organisation to help them develop a KM strategy. It became clear during the engagement that this was a very turf-sensitive, political organisation, and in fact they had two different kinds of KM initiative going on, each reporting to a different senior manager. There were all sorts of coordination and knowledge non-transfer issues, and much wider confusion and scepticism about KM in the wider organisation. They needed role and mission clarity. Despite the opposition of both senior managers, one of whom was the one who hired us we recommended that the KM teams be united under one senior manager, so they could implement a common strategy and present a common face to the rest of the organisation for what needed to be done. I argued this forcefully at the senior management team level but they disagreed. Not long after, the more experienced people in both KM teams left out of frustration, and they had to build their teams again from scratch. The result is a slightly stronger team on one side which is more active, but there's still confusion. Why do organisations seek to hire people ostensibly for their expertise and experience and then fail to act on their advice?