At the time there was a new dome proposed as part of McCormick Place (McDome), however there was a lot of pushback with things like the Bears should only play on grass and the Bears should play outside in 'Bearweather'.
Yeah the relevant design stuff was happening in like 2000-2001 which was just a very different time in terms of the thinking around what an NFL facility could and should be.
Jerry Jones' Cowboys project was a game-changer, but that was still years away at that point.
A SF dome would have cost way, way more, and the use case for that sort of facility wasn't clear yet. The CFP didn't exist, the process by which a facility like that could be selected for the Final Four was speculative, etc.
It lacked foresight to do what they did, the city of Detroit opened Ford Field at around the same time, so it's not like this was an impossible idea, but it was a different viewpoint back then.
The thing is, the Bears play 10 events a year in Soldier Field, for whom the attendees are people who drive in from the suburbs, park, and drive out. It's not that big of a deal in terms of bringing people and commerce into the city (very different from Wrigley in that respect).
But when you combine McCormick Place, the new DePaul arena, the Northerly Island pavilion, Soldier Field, the Field Museum, the Shedd Aquarium and the Planetarium, there are millions upon millions of people coming through that area annually and none of these things are connected in a way that makes sense. It could be so much more.