When a mass evacuation of Houston occurred due to Hurricane Rita, 107 people died from the conditions caused by the mass evacuation. The conditions on the roads were very very poor for those following your suggested advice of "heeding the warnings". The storm in the end was not as big of an event as it was made out to be.

It's not as simple a decision as you're making it out to be.

https://en.wikipedia.org/wiki/Hurricane_Rita#Evacuation_deat...

The governor told people to leave. The mayor told people to stay. One of them isn't going to be reelected next term...

Probably what should have happened (I'm using my perfect hindsight here..) is they should have told people living in low-lying areas to either go live with relatives or friends who were on high ground, or leave town altogether. And everyone else to stay. This would have prevented the mass exodus that clogged roads during previous storms, but gotten more people to safety.