I’m betting that has to do with enforcement of the contract. The buyer is the party who made the purchase and accepted the agreement not to refill the cartridge.
That means you’d have to go after individual purchasers as they violated their contract by sending the cartridges to get refilled. It would be much easier to target refilling services and shut them down. But they can shift blame to the consumer by offering up that they informed the consumer and that consumer went ahead anyway.
That means you are targeting consumers instead of the groups that facilitate the act which means you’ll always be behind when trying to handle the violations.
But when you shift cost of your product onto the consumables for it this is what you get.
