What are some disadvantages of Cube shaped packaging?

Cube-shaped package does not handle oblong objects well.

Cubes have no preferred "up" direction, so payload that must be kept "this side up" may not survive well in cube-shaped packaging.

Cubes are not always easy to handle.

Relative to other shapes, their center of gravity is pretty high. A stack of cubes may be more likely to fall over than a stack of flatter package shapes.