John, it was pretty obvious. Maintaining AM facilities, land, ground conductivity, guy wires, towers, interference complaints, ordinances, plane lighting, electricity, etc adds up and doesn't compute just to drive a translator. While the iBOC HD sin tax on every HD stream is a crime, it is less than the AM scenario.
The only upside of this? Less signals on the AM band might allow other stations to propagate better at night and provide more listening opportunities.