Hmm... The game has gained a reputation for being unreasonably difficult, right? Well, if there's one thing I've learned in my personal study of game design, it's that "understanding justifies difficulty." That is, the more threats a player can see, comprehend, and reasonably deal with, the more threats you can cram into any one gameplay sequence.
Obviously, that's completely thrown to the wind in the case of IWBTG. But maybe "understanding justifies difficulty" can come to encompass an entire game. That is, IWBTG is almost universally recognized as one of the most difficult games of all time, and most new players at this point are going to be drawn in by that claim. Those that do play for its absurd difficulty understand its role in the entire game, and therefore find it somewhat justified.
Maybe not. I'm just trying to wrap my own head around the game's popularity.