Maybe so, but it's traditional. Most bombs and other heavy stuff is made in government owned factories even today. Oh the guidance equipment and so forth are made by private industry, but the ordance part is made in government owned factories. The same holds for missles, motars and so forth. The famous M-1 Garand was a product of a government Arsenal (and John Garand worked for the government), as was the follow on M-14. Of course the M-1 Carbine was not, nor was the M-16. During WW-II much of the production was done by private industy, including many that had never been involved in making guns or ammunition before. Prior WW-I, most of the military small arms, and the big guns too, were made in government owned arsenals. Harper's Ferry in Virgina for example, or Springfield in Massachusetts for example. The big overhall and modification depots of the Air Force (Air Logistics Centers) are government owned factories for all practical purposes, although more of the support work in now done by contractors than was the case 30 years ago.
My M-1 was build by International Harvester, and my M-16 was build by GM.