It happens in all walks: politics, business, sports, Hollywood. As Lord Acton said: "Absolute power corrupts absolutely." I would add that it corrupts by degrees: the more a person's power is absolute the more he is capable of being corrupted absolutely. However, politicians can get voted out, business men can "fail out." Sports and Hollywood demigods can quickly disappear. Bishops are bishops for life and responsible for the eternal destination of souls. That changes everything.
Perhaps this is why today's saint (one of them), St. William of Donjeon (+1209), upon being named the Archbishop of Bourges, was "overwhelmed with grief" and refused to accept the office until he was commanded to do so by the Pope and his Cistercian superior. He was said to be preparing for a mission among the Albigensians (heretics) when he died kneeling at prayer in 1209. In his last will and testament he requested to be buried with his hair shirt and in ashes.