Subsidies exist, basically, to correct inadvertent problems, to even out inequities, to right wrongs. They make government fairer to more people. They were created as a response to the Law of Unintended Consequences.
When Cornell Professor Alfred Kahn designed the Airline Deregulation Act (passed in 1978), one of the consequences was that airlines were free to dump service to low-traffic cities, in return for a free-market economy to go where they wanted, and charge what they could get away with. Most citizens benefitted with fares that are still much lower, more people started traveling, whether it's Great Aunt Kate traveling to see the grand-kiddies or a small businessman from New York to Klamath Falls to buy doors & windows. But this guy could no longer get to Klamath Falls. The Klamath Fallses cried 'You've changed the rule book, and you screwed us.'
Congress said 'Oops, you're right, we'll fix it.' They're been fixing it, via EAS, ever since and they've done better than the military with their $4K toilet seats also available at Home Depot for a bit less. The most egregious wastes of money have been curtailed, and the average subsidy is around $78 per passenger per flight, with incentives for increasing the number of PAX using of the service.
(When you look at EAS, you have to look only at the continental 48 states. Alaska and Hawaii are so different they they skew any results.)
Government exists to serve the citizens of this country, not just those who choose to live in cities.
I now live in Florida, 75 minutes from Orlando International Airport. No EAS service currently exists in Florida, nor should it. But when I buy a Jeld-Wen window or door, I'm glad the Home Depot buyer can now get to Klamath Falls.