This is never properly explained in our histories. It all came down to the artillary and this was just after the US civil war which saw ample use of horse mobile guns. Yet the difference in range for the new steel guns were no secret. After all Krupp was selling them to anyone.
In the end it was down to one man's decission in terms of procurement. The actual battle allowed the two armies to line up in hte old style and for the Germans to use their guns to smash the standing undefended infantry for hours until they finally broke.
What were they thinking even then? When you are outranged you pull back out of range forthwith and get cover. Instead they had a rout and the war was lost. It did not have to be this bad.