I'm not sure hat's really true.
For prototypes, yes. I can get a few pcbs from jlcpcb for $10. And $20 postage. And a 2 week wait.
I can get a few pcbs from my local pcb manufacturer for £100 for the photomask and something similar for an MOQ of pcbs. So if I can manage my time properly, I get them from china and save £1-200.
But when I look at the panel costs for production quantities, they tend toward the same value.
What the chinese suppliers have succeeded in doing is rattling through a design with a lot of automation and some in-house photo-processing, and have enough volume thta they can aggregate designs without any delay. I can use OSH Park : for small pcbs, they're also cheap. But they don't do as much business so it takes them longer to aggregate a worthwhile set of orders.
What they haven't succeeded in doing is getting higher volumes as cheap. I don't know what the tradeoffs are. I think the popular chinese suppliers have been careful not to race to the bottom, but that means their higher volumes even out the same as everybody else.