Due to a homebrew exploit
At this point I think I can safely call VVVVVV one of my favorite games of all time. It's pretty much perfect from start to finish, and despite its short length, I love the mix of forgiving checkpoints and high difficulty, with exploration sprinkled in for good measure.
Sadly, the game has been removed from the 3DS eShop due to a homebrew exploit uncovered by users. Apparently it's really easy to hack the 3DS by using a certain method, and VVVVVV facilitates it. The game's creator, Terry Cavanagh, originally thought he wouldn't need to patch it several days ago, but it was subsequently pulled.