My one experience with this recently is that UPS will charge you anyway for the duty and if you don't pay they will threaten to turn you over to debt collectors even if they don't deliver the package. So I'm not sure why they in particular would care.

I had the same with FedEx. I reported it as a lost padkage at X value and they decided to write off the customs charge

It’s still an administrative cost for them, and the non-delivered packages are filling up their warehouses.