Shouldn't Air Be Free?

One of the tires on our car was pretty low on air...our hall custodian pointed this out to me. I stopped by a gas station on the way back from Waukau to get the tire filled with air. I thought air would be free, but it cost $0.50! I don't want to be that old guy, but I do remember a time when the air machines were free. How much money do they expect to make?