The lunatic conspiracy fringe was always there, but so were lots of other people, including liberals, independents, etc. The biggest difference these days is that with the advent of the internet---and lots of crazy conspiracy theorists with websties that look legit, you have many hosts lazily going with the flow instead of shooting the BS down in it's tracks.
This has gone on for so long now, that you have practically a generation's worth of listeners whose understanding of history is built on layers upon layers of rarely challenged misinformation. Good luck trying to reason with THAT sizeable faction. And in the process of pandering to that crowd, most "normal" people have abandoned the format completely. I am one of those people.