Fuji couldn't talk and he couldn't get heat, which last time I checked were the two reasons you have managers. Sure in kayfabe he managed a couple champions, but he really didn't do anything of consequence during his entire run. It's supposed to be a Hall of Fame.
The name Wrestlemania will be the draw, and to a lesser extent Taker/Batista will be as well. The difference in buys between doing Cena/Shawn and Cena/Orton will probably be insignificant in the grand scheme of things. Why not give Orton the rub instead of putting Michaels into a match where no one gains anything?