Why doesn't Lynn Thigpen get billing?

The late, great, and always fabulous Lynn Thigpen does not have a huge role in this movie, but it's also not insignificant. She's not even listed on the DVD case, front or back; Whoopi, whose role is tiny, does get featured in the cover credits, as "a surprise appearance" (hey, guys, if you announce it on the cover, it's not a surprise). Even Quentin Crisp and Eric Bogosian get mentioned on the back, and they certainly don't have as much to do as Lynn. Anyway, it just bugged me.