They didn't like the quality of the tobaccos they were finding. They felt that the ending of subsidies to tobacco farmers, coupled with the end of the auction system was resulting in production shortcuts that affected the quality of the leaf that they relied upon for their blends.
Also Mike McNeil had major back surgery and the physical labor involved in producing blends to their standard was becoming too much. Rather than sell the company to someone who wouldn't continue to produce their blends to their standards they chose to close the doors.