My neighbor might run an unsecured network. Poorly designed software in a smart tv might cause my device to auto-join an open network. In this case, locking down my own WiFi would be irrelevant to the television.

This type of behavior was the cause of new Apple Watches that couldn’t access the net over 3G (they were trapped on captive WiFi networks with no UI to disconnect). If this happened with one device, it could happen with others.

edit: split a run on sentence