Why did the bart subway start off with a card based payment rather than tokens?
I'll venture a guess....
Unlike New York or Philadelphia or Chicago rapid transit systems, which are contained either wholly within municipal boundaries or have limited service to nearby suburbs making a flat fare doable, BART is spread out over several counties and municipalities on both sides of San Francisco Bay. A token implies one paid fare at a preset price. BART and METRO in Washington are in some respects less like traditional rapid tranist and more like commuter trains or interurbans. They adapted a distance and time of day driven fare structure making it "fairer" to all riders concerned, short distance and long distance alike.