Anyway, the penalty used to be much more. I've payed over 300dkk on a 100dkk item years ago.
Amazon.com offers to take care of import taxes for you, and many of the dodgy Chinese sites offers tax-insurance.
They have to hold the package in storage, check the invoice and declare the goods, wait for the approval and then take it out of storage for final shipping. The storage bit requires a paper trail (soon to be electronic in Sweden).
If you do the declaration yourself, they still have to hold it in storage and write it off with the customs ID you provide, which is likely more work in the end.
So in any case, a non-trivial amount of labor is involved. And since it's not covered by the Universal Postal Union, they're not obliged to do it at a loss.
Unfortunately, the Danish postal service sucks and hence we now have crappy service.
If your package gets picked, there is a ~$20 administrative fee charged ontop of the 25% VAT. Most people are pretty ok paying VAT, but the implementation in this case is ridiculous.