SIU had some very good teams. Their close proximity to Chicago and St. Louis, make them a great recruiting location for a very good coach. A strong coach can recruit good players to Carbondale because of their location because they are in the middle of a hotbed of high school basketball.
However, they never stepped up like they should have when they were so good. Even when they were good, they rarely filled up their own arena (except for when certain teams played them). If their opponents were top opponents in the league, their fans stepped up. If their opponents, were poor, fans didn't step up and go to their games. When they played in St. Louis, they showed up when they were playing for championships, and when they were playing teams that enthused their fan base (and St. Louis is extremely close to Carbondale). It seems to me that they are just like MSU in the Valley.