Yes, Karl. It's a theory I too have pondered for many years. In fact, I think the same goes for a lot of posts in the MoD.
As BEagle and others have said, people stay just long enough to tick the boxes for promotion and then move on before they've really acheived anything. Even if the next guy hits the ground running, each handover results in disruption and some of the "too difficult" stuff getting quietly dropped.
Of course, who would want to be in an IPT for 10 years?