Learn More: Router has UPnP disabled
UPnP (Universal Plug and Play), also known as multicast, allows for the discovery of UPnP enabled devices on the same Wi-Fi network.
It appears that you have UPnP disabled on your router. This makes Chromecast undiscoverable by other devices on the same network. You will need to enable UPnP in your router settings. Please refer to your router manufacturer's documentation to learn how to enable UPnP on your router.