Purnell, Gregory, Miller

Of the last three coaches to take us to the NCAA tournament only Purnell was able to succeed at the next level. Purnell had always been successful at turning around programs and did it until he ran into Mission Impossible at Depaul. Gregory had minimal success at GT and Millers stay at Indiana was just short of a disaster (if you talk to Indiana fans.) Is it just easier to succeed at Dayton than the bigger schools? Is it tougher to continue success? What is the reason they they don't reach the success they have at Dayton? Is it just lightening in a bottle?