It's about maintaining exclusivity - if you sell your $100 T-shirt for $50 instead of $100, then it's a $50 T-shirt now. Even if they always cost less than $10 to make.
It's degenerate bullshit so I'm all for the EU banning it, but there is a business rationale.
I understand why a the original manufacturer might want to destroy their remaining stock to keep up an inflated perceived value. What I don't understand is why the business buying the remaining stock would want to do the same.
And if they're NOT destroying the goods but are instead using them, then the law is doing exactly what it is intended to.