Well if you want a good spot at the front then you have to make an effort and get there early. A small fishing shelter does not take up that much room and is not tall and anyway the aircraft are sufficiently high as to be seen by all. As a photographer however to get the action / rotation shots a place at the front is needed and even then does not stop others 'muscleing in' which results in people standing at the front just to keep a place.
If tents / windbreaks / umbrellas! were going to be banned then why wait until people have put them up - we all went through a security check to get in so put signs up there or at the car parks to save people the hassle of carrying them into the show only to find they could not be used.