A lot of it comes down to a mix of snobbishness, sunk cost fallacy, and tribalism.
You can't admit that your $5,000 pair of headphones sound exactly the same as a $300 pair, because:
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You'd no longer be able to pretend that you're better than the people who have $300 headphones.
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You'd have to admit to yourself that you completely wasted $4,700.
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You'd have to realize that the tight-knit community you've formed with other $10k headphone people isn't really bettor or even really distinct from communities of people with $300 headphones.
Yep. Just like the fuckers walking around with $2500 sunglasses.
Those sunglasses don't do anything that a $20 pair can't do. And they don't even look all that different.
The important part is that they enable absolutely disgusting consumerist snobbery, allowing some very vapid people to think that they're better than other people because they have the expensive sunglasses.
In just about any kind of product you can think of, there are brands catering to this kind of conspicuous consumption.