Comment by arjie

FAA grants require airports to set fee structures that enable them to be as self-sustaining as possible accounting for their ability to capture economic activity. They are not supposed to use the grants as a fee replacement. Airports, in general, far exceed the performance of US public transit systems. SFO is cash-positive even accounting for the cost of capital expenditure and on its own sees as many passengers as a top 20 transit system.

One might have instead believed that because SFO is so valuable to the region it should be heavily subsidized, but the property repeated worldwide is that valuable things are things people don't mind paying to use. Because they're valuable.