I think it has to do with the fact that a SIM card is really a smart card, which performs encryption/decryption functions on-board. You can't really copy one smart card to another smart card. In case of physical SIM cards, your provider would have to issue you a new card and re-assign the phone number to it. In case of an eSIM, it will have to be reprogrammed. What I don't know is whether for each wireless profile, eSIM uses a different set of key pairs and different ICCID.