Most of the people who are Swans and Storm fans still follow the primary code in their home city.
And the people that live on and around the divide between the two sports in regional NSW in places like Wagga and generational Canberra families still have a liking to both sports. There are people who go to both Raiders and Giants games in Canberra, believe it or not, because they like going to live sport generally in their city and there's f**k all other entertainment options in boring Canberra.
There are also people in places like Darwin, which is a balanced NRL/AFL city. Traditionally AFL, but these days more 50/50 as Darwin's 21st century population growth comes from NSW/QLD, especially with defence being a big reason why people move to Darwin. If I lived in Darwin, God forbid I ever have to suffer that indignity, I'd go to both the NRL and AFL games that are played there. I'm sure many of its current residents actually do.