It can be hard enough to find someone you want to be with when 97% of the people around you are the same sexuality. With a 3% hit rate its much more difficult.
People often want to be with others like them. Its the same reason you get Polish or Indian or Jewish areas. Brighton isnt generically gay friendly. If you go to Whitehawk (think Millbrook on steroids) then I imagine the gay population is close to zero. Down the road in Kemptown with its gay bars, hotels, cafes and saunas its probably nearer 50%.