A (digital) TV transmitter with a few thousand watts and
a well-sited high-gain antenna covers a city of 5 to 10
million people and beyond. The electricity bill is trivial.

OTOH -- the cost of installing and maintaining a cable TV
network [sic] serving 5 million people is enormous.

Broadcasting is unique and cannot be economically replaced
by cable or satellite.

You're overlooking the fact that a cable system can provide 100 channels.