The defense did improve quite a bit
Eberflus is a defensive guy. After his first season in Chicago, however, it was hard to see that. The Bears struggled in almost every defensive category and couldn't get to the quarterback at all. In 2023, the unit took a massive step forward in almost every possible way.
In 2022, the Chicago Bears were 29th in yards allowed per game. In 2023, the unit finished 12th in the category. In 2022, only the Houston Texans had a worse run defense than the Bears. However, this season, the Bears were1st in the NFL in rushing yards allowed per game. Eberflus is a defensive guy, and he's now delivering on his goal of improving the defense. It seems counterintuitive to give up the coach after he starts improving his calling card.