[sodacat]

There were a few reasons for that. One was that they were still in an animation arms-race and wanted to show off what new and probably very difficult thing they'd just figured out how to animate. Secondly I don't think they used key frames and tweening back then, it was all straight ahead. That made it easier to draw just about anything happening, but made it much harder to stay on model.

Actually, from watching it it seems like a mix of straight ahead and really obvious key frames. I guess they were developing the technique at the time.