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.
I agree that the best option was people who had options leaving early enough that it didn't cause traffic snarls. That leaves emergency services with fewer people to handle in the worst case.
Despite what I said before, I agree it's a really tricky call, especially for authorities considering a mass evacuation, which is often not the best thing. Houston has a lot of people, that changes everything.
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.