It's called fund raising, you win you can tout your success to your donors and you are creating a tradition.
Not sure if it is true but I had heard that the alumni from their heyday, the 50's, 60's, and 70's have donated a ton of money to the school.
Also, it helps with recruiting athletes and non athletes to the school when you win.
Yeah but how long has DLS dominated? They've built a tradition now, and I'd bet they'd still win a state title every once in a while in 4A. It's not like they're gonna move up and never compete. And like I said, if you don't win enough for your liking, you can always move back down in 2 years.