The Nats have a few problems. First, the have not built any sort of following. Maybe the talented players and winning will help, but curiously, in their best season 2011, they still finished 14th out of 16 in attendance. Only the Marlins and Pittsburgh were behind them.
Next, is the problem that they have with their TV rights. They have a huge problem with the O's in this regard. If people don't watch them, it will be very hard for them to build a following.
The traffic situation in that area is horrendous. Suburban dwellers don't go to the games. They are the people with money and families who would traditionally fill ballparks. They don't.
Edit: The one thing they have going for them is that the O's stink.