US already blew most of its Cold War stockpiles in their adventures in the Middle East. And much of the West's military production facilities were shuttered after the end of the Cold War. While the same happened in Russia, the difference is in Russia the MIC is mostly owned by the State at this time, and at least some arms production facilities were kept open. The US's lack of artillery shells, happened because they closed down most of the government arsenals. And you cannot just build munitions factories on a drop of a hat.