And how large is that tower? What happens if say a forest fire rips through the ground station. Tornado. Hurricane. Ooops your entire coverage is gone.
Cell towers are more distributed, meaning loosing any single tower is far less critical. (Typically, phones are in range of 2-3 towers at any given time. Unless you’re way out in the sticks.)
The land under the am tower probably costs more than the entire cost of setting up a cell. (Especially in urban areas where they can go onto rooftops of existing structures.)
But of course this entire conversation is ignoring that it’s am radios in cars. I don’t know about you but most of my day is not spent in a car. Which is turned off when I’m not using it so as to not waste gas or run down the battery.
I have a cell phone inside arms reach practically 24/7. Most people do.