Think about it like online ads. Even though you've never clicked on one and don't know anyone who clicks on them, the market is worth hundreds of billions. There are so many novel pathogens floating around the world that if humans are exposed to 0.01% of them we'll still see regular epidemics and occasional pandemics.
https://gothamist.com/news/germs-spill-from-animals-to-human...
Think about it like online ads. Even though you've never clicked on one and don't know anyone who clicks on them, the market is worth hundreds of billions. There are so many novel pathogens floating around the world that if humans are exposed to 0.01% of them we'll still see regular epidemics and occasional pandemics.