Most of the costs of building and expanding airports are not borne by the airlines themselves but by the public via federal, state, and local governments. Admittedly, most of the cost of railroad infrastructure is not maintained by Amtrak itself, but the Class I railroads are profitable enough to take on major projects like rebuilding their routes to double-stack container clearances themselves.
The FAA AIP (Airport Improvement Program) grants typically cover 90% of airport improvement projects, with 10% coming from the local entities (state/county/town as appropriate).
That program is around $3.35BB of the $10BB total FAA expense.
Expanding airports isn't done for free. Airports charge fees to airlines for use of their runways, and they lease the commercial space inside. Any subsidies that go on here are second order - certainly not $32 per passenger.
Note that airlines don't reap the benefits of airport commercial revenue, and I expect most large airports make an operating profit, but I don't believe that many airports make a profit when capital costs are accounted for.
