I spent a lot of my adult years in Toronto and in the upstate and Finger Lakes Region of New York. As Jeff Foxworthy used to say, "You are a redneck from upstate NY if you drive 65mph in the snow"! From what I have read it was the the semi's who initially blocked the road, then it got worse from there. The are a lot of people who do not know how to drive in the snow. If the snow was wet and near freezing, that makes driving more dangerous. You are also right in that people should have heeded the weather forecast.
I drove through Canada in the middle of a blizzard, and having 4-wheel drive, and gripping the steering wheel, people in small cars were passing me like I was standing still. After watching a car spin out into the median and not flip over, I thought people would slow down, but I swear they actually sped up! They had gotten well over a foot of lake effect snow, and more was piling up. I thought the whole thing was a disaster waiting to happen, yet saw very few cars stuck, or crashed, thankfully. I wanted to be home, but spending the night in a snow drift wasn't on my list of things to do.
I was so amazed at the speed people drove at... ZOOM ZOOM ZOOM... I swear some were driving near and over 70mph! One car I remember apparently hit a patch of ice, and went off the road, stopping an estimated 100 feet off the road and covered with the snow they plowed through before they stopped. Yikes...