Just checked Vail Resorts reservations website. From what I see every day on the calendar is still open through the beginning of April for Park City, Vail, and the California Resorts, with the exception of January 1-2 (which are understandably in high demand as they fall after the end of the passholder blackout period but before the end of winter school break).

Not sure if this is due to lack of snow (CA) lack of demand due to health concerns or just lack of interest. But avid skiers should have no difficulty making reservations at the resort of their choice, at least out west. Even MLK and Presidents holiday weekends have space.