Why must they? Isn’t the whole point for you to use your existing chargers and cables to reduce the amount that need to be manufacturered?Sometimes i'm really surprised by people like you, that fail to see any problems due to their blind love for a company. Doesnt matter if you have iPad, iPhone, iMac, Macbook or you have a god damn factory in your backyard that produces USB-C cables, seller MUST provide you a cable for charging a device that you bought.
I wont be surprised if somebody brings Apple to court for this due them selling a product that you have no way of charging.