system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if wifi is just a different frequency of radio signal, why can't we broadcast free wifi to everyone from radio towers (like we do with radio)?
gpt
A radio station is like a man giving a speech to a crowd. If you want to make the crowd bigger, all you need is a louder speaker system.

WiFi is more like a conversation -- your computer asks a specific question ("Can you tell me the Wikipedia article on cheetahs, please?") and receives a customized answer ("The cheetah (Acinonyx jubatus) is a large feline...") Even with powerful sound equipment so that everyone can hear everyone else, you just cannot do this with one guy on the stage. There is just no way he could hear everyone in the audience -- even if you gave them all megaphones, it would just be an onslaught of noise. Furthermore, he could only answer one person at a time, so it would take forever to get an answer to your question.

What you really need is lots of people on the stage to handle multiple conversations; that is, lots of WiFi base stations, each used by only a few people at once.

EDIT: Thanks for the gold and the nice comments. A lot of people are complaining that this explanation seems to rule out the possibility of cell phones or LTE. Well, no, it doesn't. It just says there is a limit to the number of people who can use a single cell phone transmitter at once. And yes, the frequency you use is important, as is the bandwidth. But this is ELI5.