They pick their mode of transportation based on their needs and priorities. Taking the subway works when there’s a stop near your home, a stop near your destination, and you have all of the time necessary to wait for it. If these conditions aren’t met then you need additional transport to and from one or both ends of the subway journey.
There’s also the matter of weather, which is less obvious to people who don’t live in locations that see extreme weather or deep snow. Safety and cleanliness is another issue depending on the location. There are cities where I’m just not going to take my kids on the subway if I can avoid it.
People who hold up numeric metrics like number of people transported per unit area don’t understand why people prefer to hop in their car and go to their destination rather than spend potentially far more time navigating a crowded subway system.