The movie trailer gives you a preview of what to expect in the movie.

So if the demonstration gives you a preview of acrobatics, silly showmanship and breaking boards then that's what you should expect.

Martial arts existed quite well without demos and demos used to exist a long time ago as well just in different forms.

These demos are just a result of modern culture and marketing - everything needs to be cool, mystical, kung fu movie-like or nobody will come to our school!