Probably has little to do with anything we think.
by building the trolleys as low as possible the CG of the sacks are lower for transporting.
also having them so low that the bags have to drop from the fill chute this utilizes gravity to settle the grain or product inside insuring there would be enough head space to lace up the sacks.
the old bulk feed store in a town near to where I grew up would fill the gunny sacks then a guy would lift them and bounce them hard against the floor before sewing them up. Other wise if he didn't there would not be enough head space in the 100 lb sacks of grain to sew them.
The peanut thrashing machine we used to use from the coop had a sacking feature on it the plate the sacks rested on while being filled had a rotating cam under it to cause the plate to slap the bottom of the sacks this knocked dust out of them as well as settling the peanuts. The newer thrasher the peanut dryer coop provided just used a chute to blow them in bulk to a container then we would shovel a few sacks full to keep. Pretty sure we made less money selling bulk than by the sack but a lot less work.