Explanation
Before creating a network interface, you must have an existing virtual network in the same location and subscription you create a network interface in.
If you try to create a NIC on a location that does not have any Vnets you will get the following error: "The currently selected subscription and location lack any existing virtual networks. Create a virtual network first." Reference:
https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface