.22 ammunition uses rimfire priming, which requires unique machinery which as I recall no US company dared to buy more of, as mentioned in the Wikipedia article

.22 ammunition uses rimfire priming, which requires unique machinery which as I recall no US company dared to buy more of, as mentioned in the Wikipedia article you linked to. Existing US 3 billion rounds per year + foreign imports couldn't keep up with the demand, which also seems to have included a lot of new gun owners, buying .22 models like their main guns or conversion kits for cheaper practice. Perhaps related to this scam, I don't remember any company other than Remington building out a major increase in capacity, that article mentions their $32 million plant expansion. Companies were reluctant since they didn't know when demand and supply would get back in sync, I would also wonder if smokeless powder capacity was a factor, there aren't very many companies that make it.