This is because you can only self process orders for delivery in New Zealand. 
We are able to ship sandals to you outside of New Zealand, but we must use a special back office process to do this.  GST is zero rated on export sales and freight is always charged - how much freight is charged depends on which of many options available the purchaser selects and the size and weight of the sandal order.
Please refer to the Help / FAQ question relating to "I don't live in New Zealand - can I buy your sandals?"