When cars did become more dependable and affordable around the 1920's, it made it possible for people to choose to live on the more affordable undeveloped land between the arms of the starfish and even further out. It is a problem of moving people from many locations to many locations, not one of moving a crowd from one spot to another. Due to our freedom of choice and our desire to own our own single family house as far away from our neighbors as possible, we are spread out. In Seattle, our areas biggest employers include Boeing, Microsoft, regional and local governments, K-12 schools and a multitude of small businesses. The last time we checked, there weren't many of these conveniently located at either end of the proposed, immensely expensive light rail tunnel under Capitol Hill.
Transportation is one of the most politically influenced areas imaginable.
Let's examine some of the dynamics. The public is desperate for transportation solutions and their desire can be compared to that of a dying person seeking a cure for his disease - anything that offers even the slimmest chance of solution, no matter what the cost, is worth trying. Because light rail systems are very expensive the contracts to build them are huge. There are only a handful of companies in the world large enough to build and bond a major light rail project. These few companies would much rather sell what they already are building than risk innovation.