The entire Soldier Field reconstruction was a disaster which should give the Bears an out. The design was constricted by keeping the landmark status which limited seating and design. After the fact, that landmark status was removed. It represents unnecessary revenue affecting building stipulations that have limited the profitability and accessibility of the facility. It may be an out but really, the rent is negligible.
Bears lease is only 5.7m a year and that could more than be made up by simply offering naming rights on the new venue. They also gain the stadium itself and a lot of extra seating, concessions and parking revenue. Imagine how much they lose to $8 dogs, $5 soda $10 beers and parking that would now be theirs instead of the city's.
It's a huge financial win for the Bear (depending on building concessions) if they pay every penny of the existing lease.
