think he has tsukiyomi because his genjutsu was visualized as this dark void type deal.but if you notice, everytime he uses it, it specifically says "sharingan genjutsu". why would they translate itachi's as tsukiyomi and then sasuke's as sharingan genjutsu? that makes no sense. on top of that the whole point of the MS is to have different specialties. sasuke is able to manipulate his amaterasu better because thats what his right eye does. on the other hand, itachi's right eye didn't do that, thus his control over it was much less. instead of having that control over amaterasu, he got tsukiyomi. just like both obito and shusui's eye only have one ability in each. obito's eye is versatile in it's use of said one technique, but it is the same technique.
