Probably a combination. The clear air in the area, coupled with moving pictures having been pioneered by William Friese Green (he has a blue plaque on his former home in MIddle Street - I'll check it is Middle Street shortly.
There's more information here:
When thinking about the filmmaking industry you wouldn't really think of Shoreham as being part of it...
www.shorehamfort.co.uk
I was correct. Here's another article with the photo of the plaque:
Film and cinema in Brighton & Hove.
www.brightonhistory.org.uk