Too much atmospheric clutter (Canadian smog, geoengineering particulate like silver iodide, aluminum sulfate, strontium, etc) for line of sight to carry that far
In the Dakotas, there is an AM radio station (KFYR 550AM) that broadcasts out of Bismarck that can be picked up hundreds of miles away, even as far as nebraska. If the world were a ball, the transmitter would need to be over 2 miles in the air to be able to clear the crest of the surface of the globe to transmit that far. The only way that radio transmits that far is because it's flat.
en.wikipedia.org