A few things. Cost is number one. If the Forage or Service Cap become a mandatory issued item, the cost of headwear goes up, therefore the budget for service dress uniforms needs to increase, or savings need to be found in other uniform components (gabardine moves from issued to optional purchase for example).
Second, just deciding between the two. 1C/D patrol dress is an authorized optional order of dress, with a Forage Cap. Do we issue that forage cap for wear with No. 3 and then parts of an optional dress item are now issued, or do we only do the service cap in khaki and members still have to purchase a forage cap for their patrols (if they decide to get them or a unit buys them with private funds).
Third, usage. If we go with forage and service cap, how much will they actually get worn? if we do both, outside of offices with service dress as dress of the day, most members won't ever wear the service cap, as the only time they really put on service dress is for events like remembrance day, and would thus wear a forage cap.
hats are a very touchy subject in the army....