Since these high end cable mfg. are many times using ultra expensive audio gear to conduct listening tests, maybe when the plug a $100 vs a $5 vs a $15K USB cable through a $50K DAC through a $750K system, they hear a noticeable difference. That's one thing I do notice when I first got into higher end audio. Whenever I replaced one piece of gear with something significantly better, it then revealed the rest of my system where I had to then upgrade another component.
For all we know, maybe these ultra expensive DACs reveal a cheap cable vs a more expensive cable because of something we're not taking into consideration or being measured. I don't use a super expense DAC, but I don't mind spending $100 on a USB cable for a little peace of mind. $100 is kind of my personal limit on how much I would pay for a USB cable. I have bad luck with cheap cables with my computer system where cheap USB cables simply don't last that long before they crap out.
I ran a Black Magic disk speed test comparing a cheap USB 2.0 cable and a $100 2.0 cable, both were the same length and damned if the more expensive cable didn't perform better. Was it a HUGE difference? In my specific cable comparison, it was noticeable and repeatable as I couldn't believe that there was THAT much difference as they were supposed to be both USB approved, yada yada yada. But it was a good 5% to 10% better read/write tests on average, some even better than that. I was surprised, it at least gave me a reason to justify the extra money spent. Years later, I gave up using USB 2.0 drives as it's just too old of a standard to even bother with.