My hypothesis is that the $1000 cables help sell the $300 cables. I’ve seen comments to the effect of: “I’m not fooled by those $1000 cables, so I saved my money and got the $300 cables instead.”

In other words, they got fooled.

What’s happened in electronics is that there’s a cutoff, above which the audio quality doesn’t get any better, but that cutoff is much lower than anybody can believe. So the psychological cutoff is higher than the physical one, and a role of marketing is to raise that cutoff even further.

it also puts a market value on said placebo effect...

This may be an unpopular opinion, but if people believe they can hear a difference in their $1000 cables, and they enjoy purchasing and testing them, I'm inclined to let them enjoy themselves. I have a basic hi-fi setup with rational cables, and enjoy the cost savings, but to each their own.

I feel the same way about wine. At a certain point, it's not really about objective improvements, it's about vibes and lore.