Subway systems are absolutely useless unless the stations are spaced very close together and there are other means of transit from the station to where you want to go. There is no point taking the subway when you need to walk several miles from the station to your ultimate destination.
There are only a handful of cities in the United States dense enough for a useful subway plus local transit system to make sense. New York is one. Chicago is borderline. Los Angeles is far too spread out for such a system to work.
On the other hand, if I can turn my car into a subway train and then get out of the tunnel and drive to where I want to go, that's actually useful.