It’s regularly 3% duty plus sales tax so around 8-10%, it’s just you didn’t account for it in your math.

Yes I understand it’s still cheaper and a good buy if you happen to be there on a trip and don’t have to account for airfare. Oh and don’t even think of bringing items without declaring them to US Customs or trying to defraud the US tax system by declaring a gift or low cost item. European VAT declaration that have you that tax free item reports it to US Customs, so they know you bought the item and how much you paid before it reaches the US, the fines are pretty bad and it is a criminal offense. Here is more info about all that from a few years ago.