SB Nation's Buc 'Em blog lists several possible reasons for Tampa Bay parting ways with Jagodzinski:
Jags didn't want Leftwich as the QB - A once unanimous decision, Jags may have fought it or rethought the decision to put the great, immobile object behind center. Jags offense is based on runs, mid-direction and play-action and perhaps he felt Leftwich could not provide the moderate mobility needed on some of these plays.The offense was stagnant in the preseason - This is a HUGE stretch, as the preseason typically doesn't show much and the Bucs were able to move the ball at points. In no way did their offense look worse than previous years, and without our top two wide receivers, and all of our running backs, I don't see how this determination was made.
Freeman and Olson are close- Josh Freeman has gone out of his way to mention how Olson has mentored him but I hadn't heard him talk about Jags.
The first one seems to be the speculation du jour around the internet. Jagodzinski didn't want Leftwich running his offense. He may have voiced his opposition loud enough to get himself dismissed.