> I wonder if the density of enthusiasts that need PCBs made is so low that the entire market is captured by only one or two companies based off China

The sad answer is that yes, it is that low.

The better answer is that as PCB manufacturing gets more hands-off, we can look forward to some "PCB totem" somewhere in your city, like those self-service photo printers that exist now.

JCLPCB and who? Having a board made and assembled was both great in speed and effort, and terrible in cost markup when you add tarrifs on a $50 uc at 5 board minimum.