Also, traveling across the Bay (and between other co-terminals) is specifically included in United's contract of carriage (I think) as not being covered by United's largesse. Maybe that's an arm's length contractual term yesterday and an unfair junk fee tomorrow; who knows . . .
Under Rule 24.E.2(a) UA is obligated to transport the passenger to the connection point "at no additional cost to the Passenger." There is nothing in Rule 24 that requires the passenger to pay the cost of ground transport to a co-terminal. You may be thinking of Rule 24.F.1(b) which excuses UA from providing lodging when it diverts a passenger to a co-terminal of the passenger's destination.