why did humans stop building with squared bricks and opted for rectangular ones?

the image bellow is of a Babylonian wall. as you can see they used squared clay or mud bricks which were arranged in a stretcher bond pattern but in both axes. this allows for building very thick walls without an English or Flemish bond. this pattern is very common in ancient Mesopotamian buildings. but almost absent in later buildings.

in later and modern brick works I see rectangular bricks used in an English or Flemish bond pattern to give more strength when building thicker walls (otherwise the thicker wall would be just two walls held together with mortar).

why? why did humans go from using squared bricks to rectangular bricks? they seem more handy to me.