This is an EXCELLENT point. Last year at a local contest I watched a band play a show with a fantastic repertoire (1812 Overture, Sleep, and Eine Kleine Nachtmusik) and had a decently difficult visual book. IT WAS THE MOST BORING THING I HAD EVER SEEN IN MY EXPERIENCE OF WATCHING MARCHING SHOWS. The music was mechanical and out of tune, but all the notes were correct. The body movements and step outs were lifeless "hokey pokey-esque" flailing of limbs, and did not communicate the expressive, graceful, or powerful intent that the designers had in mind AT ALL when the show was being written. It is all these reasons why this band did not make finals at the festival. This is testament to the fact that you can be given the opportunities for success by your directors and designers but then you simply don't put an ounce of feeling into it. It was mechanically correct in almost every way, it was just boring as heck (yes, they made 1812 boring...).
Also, I agree with Xenon that cost is a huge limiting factor. My friend took a class at Tanglewood this summer about the economics of band programs and it turns out that The Woodlands spends ~$800,000 in a year when they attend Grand Nationals (this is apparently the most in nation, $300,000 ahead of #2, Avon High School, who spends $500,000 a year). This is just excessive for anyone, especially a band that is not THE best. I don't even want to imagine what the band fees for The Woodlands must be!!! Mine are only like $300 a year....
UIL, in my opinion, should create a separate division for military bands. Why should they be made to compete against corps bands? They are two COMPLETELY different things. Each style has different ideals and paradigm. Military is marches and perfect visual, corps is...everything else. They aren't the same and, as such, they shouldn't be judged the same. The only one I know of that has ever made state finals is Kingwood back in the 90s, which goes to show that they really don't have much of an opportunity for success. They should have their own Area and State competitions that tailor to their specific needs. That's just me though.