People along the Gulf Coast are a little jaded to hurricane evacuations. 9 times out of 10, you can simply ride out the storm. So, that played a part in it.
There are also plenty of people who simply cannot get out. The elderly, the sick, people who are too poor to own a car etc. Then you have the random people like tourists from other countries who are simply in the wrong place at the wrong time.
A lot of factors in why some people stayed.
We have elderly cousins who live (lived) in the 9th ward. They've not owned a car in years - NO is so insular in some ways. They took buses or cabs or walked. They went to the superdome, so initially we were somewhat reassured as to their safety. Now we are very worried and they've not shown up in Houston yet. An uncle drove from Austin to Houston hoping to find them.
We also have cousins in Gulfport who said, "I sat right here through Camille and I'm going to set right here through this storm". (You have to imagine a very heavy southern accent to get the full effect.) The Red Cross called earlier today to tell us they are safe in a shelter - their home is gone. I think a lot of people who survived Camille thought of it as the worst that could happen.
We are still missing four "maiden aunt" cousins, the youngest of which is 66, the oldest is 92. They were going to go to a shelter, but we've got no information as of yet.
Damn.
I hope all your relatives turn up safe and sound.
I don't think most people who stayed bought into the whole "end of the world" spiel from the media. People have been crying wolf about hurricanes for ages. Usually, you end up with a flooded basement. 9 times out of 10, the worst-case scenarios do not happen.
If they are your family...why didn't you go get them?