That’s because they are the biggest liars I’ve ever met. They’ll say anything to get you into surgery.
I have to agree, especially when it comes to the so called 'functional' improvements. When I first consulted a surgeon about my bite over twenty years ago, he said my teeth will fall out, I will have digestive problems (because of not being able to chew properly...), speech problems, TMJ pain and so on if I do nothing. I did nothing except orthodontics and never had any problems with anything. On the other hand, practically everyone that has surgery will have problems with numbness, pain, sometimes speech and eating and so on. I'm pretty sure the surgery causes more functional problems than it solves. The main reason I can see for getting it, for most people, is to improve their looks - and in that case we need to understand the potential aesthetic drawbacks like nose changes etc.