hazlntskier Before about 20 years ago I never heard of ski areas closing because of weather unless the power was out or absolutely no snow or ice on any part of a trail. I always thought it was due not wanting to issue refunds (multi-day passes etc.). I believe Wildcat was the first one to close because of temperature.
Not hearing about it doesn’t mean it didn’t happen. Which might have more to do with the internet and the changes in how quickly information spreads. Before twenty years ago, there were still many resorts that didn’t even post current conditions on what passed for a web site back then. You used to have to call a “snow phone” to hear a recording about conditions.
Fact is, at -20F and high winds, it is dangerous for both employees and for guests to be outside, especially on a lift that could have an issue resulting in an evac. Surely ski areas have closed for cold at some point prior to 2005. But, perhaps closures may happen a little more frequently, out of fear for law suits. And, I am sure employers really do care more for their guests and employees now than at some points in the past.