I think the biggest factor is that there's no patent laws in China, and everything is reverse engineered.
Having said that, it's a catch can.  A low pressure can with an inlet, an outlet, and something to make the heated oily bypass condense.  It's not rocket science, and it doesn't involve intricate micro-tolerance moving parts.
The catch can I bought from Ebay looks nicely machined, everything fit together, and I saved some $ as a byproduct.  It still wasn't 'dirt cheap'.  But it just goes to show how grossly overpriced some of the things for our trucks are...