And I would contend they aren't, you just haven't performed the right testing to show it.
For fun I just plugged in one of these freebie cables into my headphone amp, not much difference in apparent quality of what you reviewed (heck, mine has gold plating), and is a class of cable that is part of your generalization.
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Wow, just wow. 60 Hz hum galore, nearly as loud as the music playing itself, and the cable is nowhere near a power line. I didn't expect it to be this bad (was expecting a quiet background hum), but these were atrocious. Then I plugged in a (inexpensive) shielded cable of the similar type, no more hum. Would you like me to ship this cable to you for more extensive testing? I unfortunately do not have a precision audio analyzer sitting around.