My concern with radio is energy consumption. Transmitters are only about 50% efficient. So a 50kw transmitter is likely slurping down 100kw of power, 24/7. That can be incredibly wasteful, depending on how many people are listening at any given time.
Compound that with heavy advertising (for some stations) , and the "duty cycle" is even lower. It reminds me of those billboard trucks that drive up and down las Vegas, just burning gasoline, creating traffic, so you can see their ads.
Not that many 50kw stations.
Efficiency is up, more in the upper 70%'s now days. (of course broadcasters will use a transmitter until it is unfixable, so there are some 50 year old units still on the air). Each user requires a 9 volt battery to listen (maybe a bit more...)
Compare that electricity with the streaming cost. The streamers computers and routers. The infrastructure cost for the internet (not all amortized to streaming, of course). The desktop / laptop / phone electricity for EACH user / subscriber.
Once you hit a certain audience size, broadcasting is more efficient.
Note: I agree with you on the billboard trucks. A waste.
Yes, audience size is key. If there was only 50-100 listers (say late at night), does it make sense to run a 1kw microwave for each listener so they each can hear Nickelback?
I know it's more complicated than that, if they shut off the transmitter at night, they would lose listeners in total. I just think it's wasteful compared to other forms of communication.