Epic definitely stops selling passes too around Thanksgiving I think
they do it so when your average family flying in from Texas or whatever for a week at the resort compares a lift ticket price with a pass and calculate that they all should just buy passes to save $$, Vail/Alterra doesn't want those vacationers to do that math so they eliminate the option
Season passes are for the planners, and tickets get forced onto everyone else who shows up once the seasons underway