A "TV License" is one of those things I alway assumed people were making up to satirize the claims of over-regulation & bureaucracy in the UK. Finding out it was real was a mixture of hilarious and sobering.
If you were to design such a system in the 2020's, you could just put a DRM scheme on your broadcast and demand payment only from the people who actually want to watch that network specifically, but that technology wasn't yet available when such systems were designed.
Another claimed benefit of this way of doing things is the government's ability to produce programs that aren't commercially viable, e.g. targetting specific populations, minorities who speak a niche language, distributing important public information in a non-sensational way etc.
Most of these points are moot with the advent of the internet, though, hence why many countries want to or have abolished these licensing systems.