What most people that don't live in an area impacted by hurricanes don't realize is that much like this hurricane they change course on a daily basis. In 24 hours, the landfall prediction changed several hundred miles. Employers and schools do not shut down because hurricane is in the Gulf. Most Houston residents are employed in the pretro-chem and refinery industries. Those plants are designed to run 24 hours a day, 365 days a year regardless. Power loss and flooding does impact that.
Most non-residents say just leave. Well, you can't leave every time the wind blows. It takes quite a bit of effort to secure your home. Everything outdoors that is not nailed down has to be moved indoors, everything. During bad storms, Cat 3 or greater you have to secure the windows. Most say leave if it is Cat 3 or greater. You have to shut off all utilities. Our home was rated for 130 mph winds. It was not uncommon to have 30-40 storms 10-15 times a year. There were typically 1-3 storms with 60-65 mph winds that where simply rainstorms. We slept through many storms with high winds an never knew they happened till the next morning.
If you have animals, you have to tend to those. There are a tremendous amount of folks with livestock that have to be considered. They mark the livestock with owner information. That is every head of cattle, every horse, goat, sheep, etc. has to marked in some way so that you can get them back should a flood happen or fencing is compromised. We had two horses when we lived there. You don't want to get trapped in traffic with horse in trailer with nowhere to take them off the trailer. You can only carry so much water and hay.
Gasoline for your vehicle is another issue. There are only so many ways out of town. Gas stations are overrun. If you leave early, you have to have a place to stay. Hotels are not cheap. How many days do you stay? Where do you go? How much vacation from work do you have? Do you have enough vacation for every storm that enters the Gulf of Mexico.
@Volprofch05 stated that he didn't know why the roads were below elevation. The Houston area is flat. It is only 30-40 feet above sealevel for a very long distance. The roads are designed to help divert the water away from areas the best that they can.
I lived in the Houston area during Harvey. We got 35.6 inches of rain in a 4 day period. They said that if you spread the water dumped on the Houston area across the continental United States it would be 11/16 inches deep. That's a lot of water. People would leave their home only to find a river across a road. They would turn around and find that the river was across a road that they had just traveled less than 5-10 minutes prior leaving them stranded hoping the water didn't rise anymore.
Apathy is major problem. After many close calls or false alarms, many play the odds and don't leave. Noobs typically leave at the first threat. But for all the reasons above, they don't it the next time. When one makes a direct hit, many are ill prepared. It's not an easy decision. My wife said yesterday after talking with some Houston area friends, "I'm glad we don't have worry about Hurricanes anymore".
To all the VolNation Houston area folks stay safe, and batten down the hatches.