Why does jingdong courier require that the price can only be insured according to the original price of the item?

Because the service rules of Jingdong Logistics are clear:

Customers choose insured price when delivering goods, and pay the insured fee according to the declared value of the goods. If the goods are damaged or lost due to the responsibility of Jingdong Logistics, compensation shall be made according to the declared value and the loss ratio, with the maximum not exceeding the actual loss amount of the goods. If the insured fails to fill in the declared value or fails to pay the insured fee, compensation shall be made according to the uninsured price.