Stadia only generate revenue if they are part of a larger development initiative, a la Coors Field and LoDo in downtown Denver, or Petco Park and the Gaslamp Quarter in San Diego.
If S.A. wanted to build a stadium smack dab in the middle of downtown in a place where they could get that many more people to spend time and money downtown, and simultaneously have developers invest to put even more restaurants and shopping and other attractions down there, that could work. But it seems that everybody freaks out at that those kinds of proposals.
Likewise, if a stadium were built around the Quarry, and developers had a plan to expand the area to serve the huge influx of people before and after the game, that could be a workable plan. But everybody has to be on the same page.
In and of themselves, stadia don't make any money. If you build one in a crappy industrial part of town, people will drive in to the game, and leave right afterward. SBC Center is a prime example.