I was not here at the time of the demise of the Key, but from all indications the highway lobby had achieved such dominant power politically there was no chance. The downtown SF power elite obsessed on becoming the Manhattan of the West and the electorate suffered from an airhead "Jetsons" mentality. Remember Bechtel promised vactrains, very much of the order of Musk's hypeloop, to the voters as part of the BART measure campaign. The ordinary joes had been indoctrinated that railways were obsolete, old-fashioned. The automobile dominated the American economy then as now. Probably more, since we have Apple I-Crap competition for the masses' dollar now that we did not have then.