MMH is a VERY finicky airport. Mountains, very high minimums, and winds that can cause severe turbulence.
At the time the flight was scheduled to depart, the visibility at the airport bouncing between 1/4 and 2 miles visibility. I can't find a forecast for the time period, but you can bet that it was pretty close to what it was currently. Either way, the visibility was WELL below what is required to even depart.
Fastair notes the number of cancellations. This is pretty true. Like I said, it's a finicky airport. Heck, ASE is a walk in the park compared.