You still have to get to and from the stations themselves, and the dependability of transportation arriving on time and proximity to your destination plays a big factor.
The metro area I went to college in had a light rail train that ran from downtown to a popular tourist destination. To get there, though, you needed to catch a connecting bus ride.
It is a 15 minute trip by car, but an hour by bus+train. If the bus ran late, it would actually be faster to ride a bicycle all 13 miles.
The metro area cities want to add more trains because it is the progressive thing to do, but ridership on one of the lines is abysmal, and the other lines aren't utilized as much as they could be because people feel unsafe on them and are disgusting- smoking cigarettes, drinking hard alcohol, food all over the floor, loud music, the occasional gang posturing or aggressive pan handling were all cited by locals in a survey as to why they chose to drive instead.