A second bridge would probably go a lot further out than Potomac. It would probably connect with the Route 28/Dulles corridor, or go even further west, perhaps use the White’s Ferry site, and connect through Leesburg/Ashburn. The opposition is from people in Maryland who don’t want to see Montgomery and Frederick Counties be completely overrun with sprawl development. That means drawing a development boundary somewhere. A second bridge would blow up any prospect of holding the line.
I child could look at a map of Monkey County MD and see the logical extension of I-370 west would be across the Potomac. It’s just common senses. A real bad case of NIMBY and big money influence.