I played in the Montgomery Street station in SF’s Muni system back in 1996-1998 with a string quartet. We routinely made about $40-50 bucks each for an hour after we split it 4 ways. DC is just not used to street musicians.
Also, a string quartet gets more notice, I think.
Finally, I should note that we also tried an experiment. When we dressed shabbily, we would make less money. When we dressed semi-nicely, like we were doing it for fun, not because we desparately needed the money, we made a lot more money.
Well, SF is used to Sax and Violins right out in the streets........