Probably the same reason paper isn't square and you don't see square totes/boxes/bins in stores. Square just doesn't work well as most objects tend to be of a rectangular footprint. Having a long and short side gives more options when packing something in the same area/volume. If in the same space you had the option of the same volume and same quantity of containers but you had to pick square vs rectangle, rectangle is going to be the winner most the time. This general trend does not apply to liquids and gases.
Not saying options are bad, but problem when looking at tooling up, they knew people would want rectangles over squares, so they went that way.
Having just been doing some cleanup/binning of stuff, finding myself putting some stuff in some small ziplock bins, those semi-reusable things for food, but also good for small HW and such. They are basically the size you asked for. Sounds great at first, then you go to put a collection of them in bigger bins and they just don't pack.