Manufacturing new munitions takes resources, a skilled workforce, production facilities, and most importantly time. They can't conjure weapons overnight out of thin air by simply throwing money at the problem no matter how many billions of dollars of profit stand to be made. For now they are reliant on whatever they still have in stockpile, which is probably not as much as you might assume, given the fact that the West's military industrial complex is deeply infected by the neoliberal disease and knowing neoliberalism's propensity for "just-in-time" supply chains.

Honestly I was thinking the other day, I do not think you can get a job more than 2 steps from the MiC in the US. I think the only industry we have still is the price gouging war profiteers