Because we’ve pissed away our manufacturing base. We no longer make much of the tooling required to make products like weapons...
Germany, however, still makes a lot of machine tooling.
Actually, we now have more weapon manufacturers, especially of Stoner-patterned guns like this IAR, than we have ever had before. Raising demand in the face of import restrictions (try getting one of those dirt cheap Norinco AR15s) has created an environment in which every other machine shop is churning out their own receiver sets and bolt carriers groups. Anyone with even the most basic milling machine can purchase forged receiver blanks from suppliers like DSArms and produce serialized firearms faster than a custom wheel shop can turn out tire rims. Our domestic small arms industry is booming.