This seems to happen a lot to really talented people, but her body of work speaks for itself. From young and sexy in Cool Breeze to Martin Lawrence's mother in Welcome Home, Roscoe Jenkins, Margaret Avery seems to be the piece that makes every movie complete.
And this couldn't be more true than in her Oscar nominated role as Shug Avery, the troubled Blues singer in The Color Purple. It's probably her most memorable role and celluloid proof that she is underused and over looked. And although she stole the focus in other roles like Which Way is Up and the made-for-television movie, The Lathe of Heaven, Margaret Avery always seems to be better than the material she is given.
Without knowing her, one can only speculate as to why better opportunities didn't follow after The Color Purple, but my guess is that she just got lost among the sea of talent that never makes it into the mainstream blockbusters. And it's your loss, Hollywood.