Because what everyone wanted in 2001 was a sequel to a 1987 mecha OAV. Oh wait, no they didn’t. They really didn’t.
Seriously, why would you have a sequel to a Toshihiro Hirano show, a sequel that is being directed by Toshihiro Hirano himself, but not get Toshihiro Hirano to design the characters? It’s a niche enough prospect to begin with, so why wouldn’t you at least make it look familiar to the old fans of the OAV?