Behold the mighty Spheramid!

They're also leaving almost half the volume in bits on the ground.

Volume of a sphere of diameter 1 = ~0.52 Volume of a cube of 1 unit = 1 Volume of a cylinder = ~0.79

So not only are they not doing the required job. They're wasting twice as much time and material than needed to make the job easier...

And you could still build a pyramid with cylinders...