I can’t really speak for NYC or LA, since I have never lived in either one for any appreciable amount of time, but in Chicago, it’s because of vastly unequal access to public transportation. Housing demand is skyrocketing in neighborhoods near L train stations, while the population is dwindling on the west and south sides of the city where train service is virtually non-existent. Nobody wants to commute to work via two 45-minute bus rides, and driving to the loop from those far-flung neighborhoods is cost-prohibitive for all but the wealthiest people (not to mention that it won’t save you much time, even if you can afford it).