As a native Texan, I can't really defend this, but I can try to explain it.
There are towns and cities in Texas where every time there's a home game, the stores, restaurants, gas stations, the movie theaters, and motels all fill up. This is, culturally, a big thing. Sure you can mock it, but I'd rather see people get excited about some young people in their communities doing something than get that excited about some fake professional team staffed by millionaires who aren't even from your region.
Also, it makes people rally behind a common point of interest. It makes communities feel like, well, communities.
I'm not saying it's a completely good thing either. I was a nerdy kid. I drilled computer science and math and English as much as the athletes threw balls around, and no one ever came to my meets. Granted my meets weren't fun to watch either.
But because it is what it is, a lot of communities, for right or wrong, see these high school football stadiums as "investments". To a degree that's sort of true, my own high school football stadium was used at least once a week for some other event and at certain times it was open to the community. And it does drum up some local business. But rarely does the community that paid for the stadium actually see a positive return on its investment.
I think it also creates a race to the bottom, because everyone tries to outdo the other.
Also, Texas or not, you will always have better luck getting people to financially support something they understand and like, and the more common the interest is the more money it's going to attract. Let me put it to you this way: I appreciate the pressure and intensity of competitive calculus and I like a nice football game once in a while too. But for every 1 of me, there's 1000 who like the football, a lot more than I do, and think calculus is a store that sells adding machines.
They're just as nutty about other things in other places. One word: Lacrosse. Lacrosse people make Texas high school football culture tame by comparison. There are places in Europe where they're insane for soccer. You also have to realize we don't have the winter sports in high schools either, so the others get that much more attention.
This is pretty bad though. I used to be a stadium official both as a volunteer and for a little extra cash, and I've been in PLENTY of Texas high school stadiums that aren't nearly that pricey that still get the job done just fine. I'm not from Allen but I've always perceived it to be an opulent Dallas suburb full of rich yuppies.
