Why can't the WAN port of the wireless router get a dynamic IP?

This is not difficult to understand, because your WAN port is connected to another router.
The optical cat, which is an all-in-one machine of the cat and the router,
as well as the community fiber, is also connected to the home through the router. And so on.
Therefore, for dynamic IP, there is often a conflict between the IP address and the router's IP address. In this case, the last second digit of the router's IP address is often changed. For example, if TP is also 192.168.1.1, it can be changed to 192.168.6.1 and saved After that, it will restart, and then log in with 192.168.6.1.