I truly believe that they are buying it for nefarious purposes. That being said, it is still a serious waste of government funds. No military organization on earth would dream of supplying its troops with such a proliferation of calibers. Congress ought to pass a bill limiting Federal law enforcement and executive agencies to using only 9mm for handguns and SMGs, 7.62 NATO for rifles (both the same ball ammo the US military has to use) and 12 gauge for shotguns. Standardization would save the taxpayers a lot of money.
I’d also like to know exactly what they are doing with it. Could they be destroying it?