Why are there so many "in Wonderland" episodes? Many series that I have seen have "x in Wonderland" episodes where they have retellings/variations of Alice in Wonderland with the characters from the show. Examples of this include Ouran High School Host Club (episode 13), Black Butler (season 2 OVA 1 and 4), Cardcaptor Sakura (episode 55), and Code Geass (OVA). What is the origin of this? Is there some sort of cultural basis for this?
I guess this is because of it's overall popularity. According here,


  Alices Adventures In Wonderland is a pretty well-known work: it can be
  associated with world-crossing fantasy, drug imagery, lolita fashion
  and other aspects of Victorian England, political satire, and who
  knows what else. No wonder it shows up a lot in anime, shock horror
  (it's a frequent target of Grimmification, usually with lots of
  blood), and emo teen novels. (You know the kind — usually involving
  vampires, eating disorders, or vampires with eating disorders.)