Because Moi dix Mois is mainly all the same style and instrumentation, while MALICE MIZER songs and albums are super varied and with a lot of different instruments and sounds.
MALICE MIZER also has more dynamic and fresh composition, while a lot of Moi dix Mois is more repetitive. It's because in MALICE MIZER, there were professional arrangers and helpers with the compositions, especially for the merveilles album, while in MdM, Mana does most alone.
