We don't have 51 channels available for OTA. 2-13; 14-51 minus 37 and 51. So 48.
And yes, we need that many to prevent interference from other stations.
One high power transmitter is the most spectrum efficient manner of delivering services. Short range transmitters would require more spectrum to reduce interference. And using low power transmitters would increase the cost of providing services: More equipment, more tower rental, etc.
DMX 68' tower, HyGain HAM 5 rotator, Antennas Direct DB8e & C5, Channel Master 7777 preamp, Siemens surge protection