Plus, if we're talking military drones vs civilian drones, they wouldn't need plastic shells. That'd just be more weight reducing distance. Then again, military industrial complex would probably try to make them stealth capable, be designed by committee from 22 nation states, be micro-USB mandated to comply with EU standards, blah blah. Yeah, you're right, we'd never be able to build them here.
A skilled machinist (and the US has many) used to be able do it in any moderately-equipped machine shop.
Is there something new and magic about modern injection molding?
I just anecdotally see that in the USA, the required iterative design process is too cost-prohibitive for injection molding, and likely the same for every other trade. So multiply number of trades (designer, CAD drafter, machinist, electrical engineer, software engineer, injection molder, assembler, etc.) multiplied by the number of experimental iterative processes required to build an institutional knowledgebase... it's cost-prohibited.