It's a very good question. It's not like Siena was a program on the rise (like you could say Mason was). Hewitt took over a program that had gone 22-59 in the three season's prior to him arriving on campus, and was 66-27 in the three years he was there (that includes a MAAC championship "1999" and a MAAC regular season championship "2000" -- 1 NCAA and 1 NIT in three seasons).
Perhaps the "game has evolved" and he didn't evolve with it? His press, especially, seems rather pedestrian compared to vcu's. I don't know if that's a product of his personnel here, or his scheme.