EDIT: embellishment due to baq, this tends to be true of cities which developed before the car revolution of the 50's and 60's. For example, my city has a pretty poor average walkability score, but for where I live in the city core, it is very walkable since it is the older part of the city.
This lesson seems to have been lost for some reason but infrastructure is to be built first, destinations second. Much of the New York City Subway system, like in the Bronx, was built through farmland. Once the infrastructure was built, destinations (dense residential) was built. It has to work that way. It's not practical to expect there to be any destinations available when the subway opens- people need a few decades to rearrange themselves.
Portland should probably join that list.
In most European cities, if you get off at train station, you're in the midst of (or very close to) the city center, office locations, touristy walking sites and plenty of choices for retail or food.
In the US once you get off at the train station, well, you're at the train station, and now need a car to go anywhere you actually need to go. NYC and SF are likely to be the only exception - train stations as close as LA or San Jose are fairly sparse and have limited connections.
You can run the fastest most frequent train you can handle, and California in fact is building one between Borden and Corcoran, but the "step 2" in US cities generally involves getting a car.