Why does people stay when a hurracane is coming?

I live in Louisiana and recently we where hit by hurricane gustav and more recently by Ike. I've watched tv to track these storms since we were told about them and as soon as they said that this storms could be really bad i pick up my 4 month old, all my pets (5 cats and a dog) and headed out of the storms way...but I cant understand is why people rather stay and put their life in risk. I've been told that is to protect their home but if your roof is about to fly away you going on top and sitting there is not going to help. My grandma lost everything when gustav made landfall and thank God she evacuated with us because I don't think she would've made it. So can anybody give an answer?