It's not realistic to evacuate, Harris County has a population of around 10 million people. How do you do that, put them all on the bogged down roads to possibly die in their vehicles. The best place to be is in your home and ride it out. As a Houston resident, I'm am absolutley proud of the people in my city. Also proud of the out of town people that drove here in blinding rain to get here and help.
There are several other surrounding counties with several million people, can you just imagine how devastating an evacuation would have been.
I saw a lot of this storm first hand.