Radio Stations As Navigation Beacons

Here is something that I just don't understand. I first thought of this when I was about 12 years old. It was in the news again this week about how vulnerable the GPS system is. The signals can be jammed or spoofed and the satellites can be shot down. 

So why aren't we using radio stations as navigation beacons, at least as a backup system? 

A radio station is not just a radio station. It is also a navigation beacon. There are dozens of radio stations everywhere and the transmission antenna are in fixed locations. It is easy to plot the locations of transmission antenna because they are generally easily visible. They are essentially free navigation beacons, whether at home or over a hostile country.

A drone or aircraft could have an antenna on each side. The signal from a given transmitter would be stronger on the side of the aircraft that was closest to it because the metal body of the aircraft would hinder the signal to the antenna on the far side of the aircraft. This would make it easy to use radio stations as navigation beacons. 

Antenna could be mounted in other places, such as wire antenna along the front and back of the wings. Pairs of high frequency antenna could be mounted inside the aircraft with a metal barrier between them. This is a simple and very useful idea, using beacons that are already there. This should have been implemented decades ago.