The issue was simplicity, time and avoiding uncanny valley. Before "The Goddess of Spring", every attempt at animating a realism style produced a high degree of

The issue was simplicity, time and avoiding uncanny valley. Before "The Goddess of Spring", every attempt at animating a realism style produced a high degree of uncanny valley, at least with human characters. Traditional hand-drawn animation is also a very time consuming process. If your animated characters have more structure to their anatomy, you have more things to have to worry about when it comes to maintaining consistency of proportions and the "physics" of what your characters can/can't do. A rubber hose doesn't have a joint that can only bend in one direction, for example. When time is of the essence, and in an era where animation studies were small struggling companies trying to sell their shorts, you need to find ways to reduce the amount of work.