Your headline should state ..."stations going silent".
This does not mean they have gone out of business, packed up and gone home. Or given up in financial frustration.
Many of these have gone silent due to technical reasons that will take more than two months to correct. Happened here, to one of the FM's where I've been chief engineer for over 30 years. A dump truck delivering fill to the transmitter site moved his truck with the load raised up and caught a guy wire, pulling down the tower. It took well over two months to rebuild. During this time the station was "silent" for over 60 days. Although we eventually got on the air with a lower power transmitter feeding a temporary two bay antenna mounted on a hastily installed telephone pole, as it takes a lot more than two months to clean up the mess and construct a new tower.
Technical issues, equipment failures, weather - including everything from ice storms taking down a tower, to tornados, hurricanes, even a lightning strike, and all the rest can leave a station off the air and put them on the "silent" list.
Of course there are some who have simply turned out the lights. Some are off due to rule violations.
Also, consider there are about 4728 AM stations, and about 10,602 FM stations in the US. There naturally would be more silent FM stations simply because there are more than twice as many of them.
Numbers rarely tell the story alone.
TIB
Good point.