If they build in any of the suburbs, their sponsorship money from the Village of Bedford Park would dry up.
Also, what do you think the urban fans would do? How would they get to the games? By having the stadium in the city, you open doors for people without access to cars to get to the games.
The 78 would be developed as a destination in and of itself. There'd be more than just a ballgame / ballpark there.
A suburban stadium would just be an island. You go to the game, then you head home. That's not how the game is marketed anymore.