probably because of all these "Magnificient treasure!" National Treasure movies and shit and people think it's cool and hip to discover the illuminati in the dollar bill. He wrote the books in like the 60's though, they are seriously good. You can open the books up to any page and find fun.
For all of you idiot internet children he's the one who basically invented discordianism.
the funny thing is that most people into the illuminati haven't even read that book, and even if they did they probably didn't really get it
it's mostly a joke, but there's alot of seriousness there too. He used to work at playboy and people would send in their conspiracy theories and that book is basically a compilation of all the conspiracy theories people would send in. Along with other crazy shit.
he was also good friends with people like Timothy Leary, Alan Watts, the guy who was in naked lunch who's name i can't think of, Dr John C Lily etc.