Some people are stupid and just don't listen. Every time there's a snow storm, you get some sarcastic jerks who go around saying, "Wow, it's like people in Buffalo never saw snow before," as people go out and try to get prepared. They think that just because we're used to snow around here, it can't present problems. So these people don't get prepared. They don't have food, or gas, or meds, and then decide they can handle the storm and get stuck.

Some people were still forced to go to work. I'm not talking about essential workers either. So imagine you have to go into work because (no can't take off and can't risk losing your job), so you go in. Now the weather gets crazy here. It changes pretty rapidly at times. Not only that, but 5 minutes away might be experiencing completely different weather than where you are currently. So you could be a work and the weather could be pretty okay there. You start heading home, and all of a sudden, there are high winds, a lot of snow, and low visibility.

Finally, there are people who get into medical emergencies or have family/friends who do. Also, people who had zero power and are freezing in their homes (my brother's place was 20°F all weekend). People may decide it's worth the risk to get to a medical facility, a shelter, or a hotel because their life (or a loved one's life) is in danger anyways if they stay where they are.