This was made in the days before Pixar existed in its own right when John Lasseter and his crew were working for Lucasfilm. Despite their successes there, the animation department was in line to be axed, so they put together a business plan. It was sufficiently well thought through to attract Steve Jobs of Apple who bought Pixar for $5 million cash and $5 million in bankroll funding.
The modeling program used at the time could only produce simple geometric designs (cones, cubes, spheres). John Lasseter wanted a flexible pear shape for the characters' bodies, as is found in most cartoon characters. Eventually a teardrop shape was achieved by stretching the point of a sphere to infinity.