I understand where they are coming from. Otherwise you will definitely have people who take a metric ton of copper and slap a sticker on the side and declare that they are shipping stickers around to avoid the tariff. Of course a sane policy would be to have a "trace amounts" option in the tariff if your product contains less than a kg or less than 1% by mass of the stuff to avoid the paperwork, but the people who set this up are the kind of people who worry more about what criminals do than what productive people do. It's just plain badly designed regulation.