From searching online, I see that the salaries for math adjunct professors are about 36k. That's insanely low for New York City standards. An undergraduate business school student that graduates from a decent program will make 3x more money in his first year of work than a Math Phd Adjunct Prof. My question is: What else do these adjunct professors do to make ends meet? Do they typically take on another job? A summer job? Work night shifts at a bar?
Someone taking such a job almost always is not depending on it as the sole source of income. They may have a spouse who has a more high-paying job in or near New York City. Alternatively, they may be independently wealthy or retired, or at least have enough money to make ends meet for a year or two while they are forced to stay in the city for some reason.
Certainly, someone who takes such a job is doing it because, for whatever reason, they want to be teaching instead of doing something making more money, and they are lucky enough to have another source of income so that they can teach.