Well that doesn't make any sense either, because there is no toll at the southern entrances to SF on 101 and 280.
I'm not looking for an answer here because I know the answer. The answer is that car drivers are the most self-entitled bunch of externalists the world has ever seen. If there was any sense in this system the toll at the existing toll plaza on the Bay Bridge would have been raised until congestion disappears, but that hasn't happened. On the other hand BART fares are indexed to inflation, because only the riff-raff ride transit.