How do you know? Where’s the audit? Anyways, every single dollar and bullet spent on this war is a waste and makes America weaker.
Because they aren’t properly usable without US support. And being components of heavy weapons systems there are no likely non state actors who would want them, certainly not in any numbers. It’s not easy to sneak components of a battery of field artillery around.
155mm ammo isn’t likely to be pilfered either. The biggest market for that currently is Ukraine. One could, I suppose, steal some and then try to sell it back to Ukraine. It’s too easy to get caught though. None of that is fungible.