It has nothing to do with cajones and everything to do with being a public service monopoly.
Unlike airlines, the mass transit system in NYC won't go out of business if the workers go on strike. There is no competing subway system that will steal customers away. If DL pilots go on strike, the airline will liquidate and other airlines will pick up DL's former customers. The two aren't comparable.
Remember, mass transit is a money losing enterprise (no mass transit system in the US makes money) and is subsidized by local, state and federal gov't. Don't complain when you have to start paying more taxes to support these transit workers.