Here's the "real story."

When BART was being concocted (yes, an appropriate term, as you will see), the politicians and designers wanted to make sure that it was state of the art, and "better" than conventional urban rail. Thus, they decided to reinvent the wheel. Using proven technology wasn't good enough. In fact, having any part of the system relate to what others had done was strictly verboten. Thus, instead of having the cars designed and built by a company that did that as part of their business (Pullman-Standard or one of the European builders of Tube and Metro cars), they chose Rohr, an aircraft fuselage builder. Standard gauge wasn't "good enough," so broad gauge was used. Ticketing and signal systems designed and made by companies that specialized in rail transit couldn't be used, so they went to companies that had no experience. As a result, BART had a very long teething period. Had they used experienced manufacturers, it would have been completed faster, and would have worked properly from day one.

There's another part of the story, though not directly rail-oriented. The promoters of BART used urban mass transit systems in places such as New York, Chicago, London, and Paris as their economic models to "prove" that people would use the system. The fallacy was that the population densities in those places far exceeded the densities in the bay area, other than San Francisco and Oakland. So to compensate, they had seminars for planning officials in all of the cities that were to have stations at which they convinced them that they should rezone the land around the stations for very high density residential and to reduce parking requirements because the people living near the stations would use BART exclusively and thus wouldn't have many cars. The only problem with that idea was that people living in the suburbs did so because they didn't want urban densities. If they did, they lived in San Francisco or Oakland, not Walnut Creek or Concord. Thus, when apartments and condos were built to these high densities, they were slow to fill up and parking problems were rife. Over the years, high density residential in the suburbs has become more commonplace and accepted, but the proper way that it should have been done would have been "baby steps" over several decades, rather being shoved down people's throats.