[Tristan Lall]

Presumably they expect substantial bending loads on the output shaft end, and therefore provide strong support for its bearing.

The webbing is likely intended to maximize stiffness while minimizing material consumption. The motor end shouldn't be subjected to loads much larger than the bending moment due to the motors' own mass, so it's understandably weaker.

There are many other possible considerations that could have driven those decisions, particularly with regard to the economics of mass production. Perhaps someone from AndyMark will see this thread and provide more detailed comments.