When I visited my daughter at college, I was shocked to see that some of the restaurants didn’t even open til 1pm. Ah, to live the life of a college student… 
BTW, my daughter worked at McDonalds over the summer. They closed for 4 hours in the middle of the night because sales didn’t justify being opened 24 hours. Her shift started at 3am (to open at 4am).
Could retaining employees be a problem too? I can’t imagine the job pool willing to work at 3am is very large, and neither would many restaurants pay shift differentials. If the only people you can find to work at these times are unreliable, why stay open?
For what it’s worth, it shouldn’t be that hard to find food. Living in Tacoma, all the local Jack in the Boxes and a few grocery stores stay open all night long. Add in the convienience stores who stay open all night, and you should have enough food choices to work. Of course, they aren’t that good–but are you really gonna be that picky in the middle of the night?
I live in Houston and I know of several… SEVERAL 24 hour fast food restaurants. I live pretty close to a 24-hour McDonald’s in a fairly poor part of town. Many, many Jack in the Box are open very late if not 24 hours. I think every Whataburger is 24 hours as well, and those things are all over the place. Taco Cabana and Taco Bell are open very late as well, if not also 24 hours.
So I haven’t seen this phenomenon at all where I have lived and eaten around Houston, and I’ve been around town, it’s not just one area that’s like this.