Why do people think animal rennet is in most cheeses?

They don't take the time to research properly, I thought that too until I researched. It seems to be in really weird fancy cheeses... However my cheese is always organic/natural so there is no reason to worry. Or it could be because of Dirty Jobs. There was a episode about cheese making that mentioned using rennet, there was a small mob of people that got confused because of it. Most people(at least those I know)will reference the show upon hearing the word.