Johnson Report: Prophets W/O Honor

I have always thought it was a statement of the character, decency and political astuteness of Harry Truman that he developed a genuine working friendship with the former president that Democrats still love to vilify – Herbert Hoover . The photo is of Truman and Hoover chatting it up in the Oval Office about the time President Truman tapped the former president to head what became known as the Hoover Commission ; a vast effort in the late 1940′s to reorganize the Executive Branch of the federal government. When Truman asked Hoover, a man still regarded by many as the do nothing administrator who timidly looked on as the Great Depression ravished the economy in the early 1930′s, to head the commission many regarded it as a very strange choice. It was unusual and also brilliant/ Marc Johnson , The Johnson Report. More here. (Photo of Harry Truman and Herbert Hoover, from Johnson Report)

Question: Why are new administrations so reluctant to to use the expertise of former presidents?