In most cases rimfire production is totally separate from Centerfire ammunition production. Production of rimfire take place at independent facilities. You cant take centerfire production and convert to rimfire, or reverse. Increasing rimfire production is much more costly than centerfire and once you have spent that and you fill the "backlog" then you have to figure out how to keep all those expensive processes running. That is the double edge sword of manufacturing. It is easier to shift resources in centerfire production as needed. Make less .40,.380 and increase 9mm for example as they can use the same machinery with smaller less expensive changes being needed. Same with rifle ammo, just reduce the number of lower volume calibers allowing for the increase in 5.56 or .308 for example.
If a company is going to invest capital in new machines they are much more likely to do so for Centerfire as they can be used for multiple calibers reducing the risk of them sitting idle as the wave breaks an starts to recede back to normal. Rimfire machines are dedicated and if they invest heavily then the demand dries up they lose tons......and pricing goes up so they can pay for idle machine when it otherwise would have returned back to normal.
It really isnt a case of applying existing resources, it is really a case of intelligent application of capital with an eye towrd the long term not just a knee jerk.