Because when you order directly from China, customs only has the invoice with the retail price (unless the seller declares a lower value for customs). In the case of BambuLab USA Inc. importing from Bambu China (Shenzhen Tuozhu Technology Co., Ltd), there invoice and declared value will reflect the wholesale price (or any price if they want to cheat with the risk of having it adjusted by customs if it’s too obvious…) and duty will be paid on this.