> it doesn’t make economic or practical sense for the organisers of the fireworks display to actively exclude people from viewing it, say, by hiring security staff that will actively patrol and prevent people from looking up into the sky

It absolutely makes sense. Before the restrictions, watching the fireworks meant ensuring a crush of people for hours, and even getting away from the riverside afterwards could take over an hour. Getting a paramedic in and out of that was terrible, not to mention toilets and small children.

Anyone who can look up to the sky is welcome to do so, from hills, rooftops, balconies etc.