They most likely closed those down cuz there's now enough people using the mountain this time of year. It costs them money to operate the additional lifts, groom the additional runs, and patrol an extra section of the mountain.
It's amazing up here the bottom at the mill is great and the upper part of the mountain is absolutely great!!!! Best all year I've been up to mammoth 8 times this year and it's definitely the best trip this year!!!! I suggest getting up here before it ends..