In these scenarios, it takes time for people to realize that the situation is real, that it has implications that affect them, and that they need to take action.
For most people that takes several hours to several days.
If people have a plan, they can walk a couple of miles to get to a boat and get away.
They hard part is having a plan, making the decision, and executing it soon enough to be effective.
Recognizing that the situation really is dire and making the decision is the hard part, people don’t want to look like fools and pulling the trigger on some evacuation service is not going to be anything but an expensive proposition. So, most will wait too long.
“In these scenarios, it takes time for people to realize that the situation is real”
I agree with that. If you live in a large city You must be packed and on the road ASAP. You can always come back if things calm down.