You mean what the rain didn't get?
Of course they keep building it up, but the point is this stuff is expensive, and for many mountains just not worth the expense. It's not like hoards are going to come out. Most of the people who come early are the same ones coming two weeks later. Earlier you start, earlier you have to pay a lot of people, run the lifts, make snow that melts away. Use a lot of energy to make snow in higher temps and higher humidity.
Killington wants to open early so they go for it.