The guys on the Score in Chicago were complaining a couple months ago that the field was bad partly because there was a high school game played between games and they didn't fix it. Don't know if it's true or not.
Because Soldier Field is owned by the city of Chicago, and run by the Chicago Park District, the Bears are not the only tenent. The field is used for numerous events throughout the year. It's been reported that rock concerts do a lot of damage to the turf, as well as other sporting events.