Up until about 2 years ago it only ran on Windows, which kept most of the music-making world from fucking with it.
Up until last year it only spoke Japanese with no real English port for any of its instructions. Means that if you wanted to do something not in Japanese you had to use Japanese phonemes and katakana instruction and it was kinda tortuous.
Also, there are few things as fuckin' Otaku Japanese as Vocaloid.
now with bonus Archer clip