When Congress passed the Airline Deregulation Act in 1978 they put together the political coalition in part by assuaging concerns that small communities would lose their flights. The legislation included a 10 year transition period in which small community service could receive subsidies. That was the Essential Air Service Program, and it was supposed to last only through 1988.
There are routes being subsidized to the tune of a thousand dollars per passenger roundtrip, that see load factors in the single digits, and that while a convenience to those passengers don’t really qualify as ‘essential’.