Oh it's because it was a "thing" a few years ago in the music
  industry. Illuminati taking control of the music industry.
  Groups like Tech9 and many others would do Illuminati
  references, veiled complaints about industry troubles, the
  excessive promotion of a few over the bulk of the talent, stuff
  like that.

  Rumors flew over the internet about Illuminati connections with
  nearly ALL the major artists and for a time, kids were getting
  sucked into it, also fueled by their parents/aunts/uncles
  generation, who likely grew up on XFiles (there's a significant
  portion of GenY that are true believers in Illuminati /
  conspiracy theories / ancient aliens / stuff like that - I'm
  sure you know a few around).

  So in that environment, they're aware of Illuminati
  ridiculousness.

  The guy that makes gravity falls is _very_ wise to kid-culture
  and he nailed it with Bill Cipher - a 4 dimensional being who
  only shows up in 2D in our 3 dimensional universe, and having a
  "kids' mystery show" done with inteligence for the audience...
  even occasionally doing "gross-out" ultra-realistic gore on
  occasion. Oddly, to me, that's respectful of the audience. A
  typical 10 year old is perfectly capable of handling tear drops
  of blood coming from the eyes of mounted deer heads for a few
  seconds and such and they know it.

  It's a nice, complicated mystery story, complete with all the
  elements that made XFiles successful and all the 90s spooky
  shows like Twin Peaks, or the 2000s ones like Lost and such.
  Good formulas, well done.

  I love too that they tap into kids' natural interest in
  crytography. I loved that stuff as a kid - and they have secret
  codes and ciphers for the kids to figure out all over the place.
  It's awesome.