Your teachers are probably from California (or just recognize that ALWD is better).
ALWD used to be much, much easier for new students to use than BB, especially in terms of organization and layout. (In fact, bb's taken some of ALWD's conventions - like color-coded spacing.) Now it's just significantly easier. ALWD's written by people who teach legal writing, as opposed to law review editors (i.e. teachers instead of students). ETA: Therefore, it's easier to learn the basics of citation using ALWD. Once you have the basics down, you can switch to Bluebook or court-specific style or crazy-partner style or whatever other system you end up having to use.
Bluebook fans dislike ALWD for the same reason people who've mastered any silly system don't like newer, easier ones: they have ego invested in the mastery of useless complexity. And they had to deal with it, so why shouldn't you?