yet they could not shake the cast up a bit like in the early TOS movies?
Well they already had to do some back pedaling to get Michael Dorn back into the action each time. Sure, they could have left him out altogether, angering Michael Dorn fans. Apart from splitting them all up in promotions positions (and then coming up with an idea to bring all the ship captains back together again that doesn't reek of small universe syndrome), how else do you do a TNG movie that resembles TNG enough to still be a TNG movie?
If they promoted Picard to Admiral, people would say that the writers were copying Kirk's career path. The series already showed some movement (Bev, Wes, LaForge, Worf, Troi), something TOS never really did. And TNG didn't have ten years off-air like TOS had.