Poverty. The answer is always poverty. Evacuation is not free and never has been.
Currently sitting in the Tampa Bay area while a category 5+ hurricane comes barreling at me. I'm in flood zone D next to E so I shouldn't have any issues there. In a building that is solid brick/cinderblock construction, built like a bunker. Don't worry about me. I got water, food, and enough fat to get me through the winter as they say.
The one thing I don't have is the hundreds or thousands of dollars it would take to drive 2+ states away and get a hotel for a week. I simply don't have it. Then you have all these people in places like Missouri or Montana posting this question about why people would not evacuate. We don't have the goddamn money. It's not hubris. We SHOULD evacuate. I don't see any of the people saying this offering up a spot on their couch. We should always evacuate... somewhere other than the house of the person who thinks we should, apparently.
If I understand it every single person in the country has a designated shelter and orders on what they're supposed to do, who they help, and so forth for disasters. It's unbelievable, it could never happen in the us.
Makes me think of the Soviet Metros. The Moscow Metro was built far, far deeper and far larger than it needed to be, partially because it was built to be beautiful because useful things should be beautiful, but also so it could accomodate enormous numbers of people if the Americans attacked. The Soviets sat down and said "how can we build enough shelters for everyone?" And then did their best.
America never built large scale public shelters partially because the government thought it was too communist and partially because they figured the cities were acceptable casualties and the
people who lived there 
were acceptable losses.
yeah, it's pretty clear they could give a fuck about any of us. however, i have no doubt there is enough space for the wealthy and powerful via "continuity of government" infrastructure which is all, of course, highly classified from all us dumbass citizens because why would we need to know where to go during a disaster? after a big enough mass casualty event, they would just relax, reshape, and contract border and naturalization policy at whatever rate wouldn't overwhelm the containment and fragmentation of class consciousness.