In a few early war photographs you will see a soldier wearing his chin straps under their chin but usually it would be short of making it all the way to his chin. Were most chin straps even long enough to fit under the chin? So if chin straps were not really functional, why continue to make caps with chin straps? This seems like a waste of material and time. Also the cost of the leather and buttons was not small and eliminating chin straps could have saved brass that could have been used for more vital items.