Back in the 90s to early 2000s, I was happy to find any PCB manufacturing service willing to manufacture a single, 4-layer PCB for $100 here in the US. The price easily quadrupled if I wanted it in a few days instead of weeks.
Fast forward to today, Chinese PCB services companies can manufacture the same board for just a few dollars for a batch of 10 and about $20 or more to ship it in a few days. It costs more to ship a FEDEX envelope to your next door neighbor. Economics cannot explain how they can support such absurdly low prices, especially given their insanely aggressive marketing targeting both hobbyists and professionals alike. For instance, they'll readily sponsor any YouTuber who remotely covers electronics topics, and their ads are so ubiquitous, even laypeople have heard their names floating around.
I'd wager they are heavily subsidized by the Chinese government. The electronics hobbyist market, especially at the advanced level of custom PCB design, is just too small to support the volume needed to justify such low prices. They're low enough to make PCB-based prototyping often more cost effective and timelier than traditional methods, such as wire-wrap, breadboards and perfboards.
It leaves an open question, why would the Chinese government subsidize something as obscure and arcane as PCBs when there are a lot more lucrative businesses worthy of subsidies. I suspect it offers some China some strategic advantages.
First, their low prices obliterates domestic competitors, establishing themselves as monopolies. Overtime, nearly every PCB designed on earth will be manufactured in China for nearly every imaginable device. Second, the PCB service manufacturers are likely retain a copy of every PCB manufactured, giving them intimate and unfettered access to intellectual property.
Is this a plausible explanation?