The issue is there's a difference between where the money comes from (capex vs opex for a simplified and incorrect example). Your support areas don't get the same budget as your construction areas. And when money runs out for the year you still have to keep thinngs running.

And while I agree that excess stock costs pale in comparison to a sub or boat, multiply that by every part necessary to keep one operational, and then face all the people every year who say the defense budget needs cut.