It's less about screwing up the models as much as not needing a pool, as well as not needing underwater capable cameras. Underwater rigging for cameras puts incredible limitations on what camera is used, the motion of the camera, etc. Keeping everything dry is always going to be preferred. The motion control equipment isn't meant for use underwater either. It just makes much more sense to shoot it dry. Especially considering this was before CGI and 3D rendering was in its infancy, maybe toddler stages.