In Dressage, Cowhorse, and Hunters, you have to learn to ride to a minimum (about intermediate) standard to compete at all. In Western Pleasure, with the horses taught to crawl, that standard is more like advanced beginner, which opens up a much wider group of customers. Raising the standard to where WP horses would do 'real' gaits would eliminate some "write a big check, get on, and don't touch anything" clients. It would also make many more horses look better, and lessen the value of the few bloodlines with the temperament, body strength and conformation (like the DVD filly) to do a pretty good crawl naturally.
But people being what they are, that's not how it works.