Because nobody will buy them because there is no way you can convey the fact that being an exact clone gives more "quality" than being a cheap knockoff. It's already a hard sell a $300 android phone from a $100 android phone, though you would say there is infinitely more differences between the two, compared to two usb-ethernet adapters.

Some people will buy Apple just because it's Apple and they want "original" stuff; others will buy Apple because they read these articles and know that the parts are high quality; others will buy the cheapest one they can find among amazon, ebay, monoprice and korean websites (probably laughing at those who buy Apple parts).

I don't think there's an easy market for "non-Apple and midprice".