Buh bye!
My guess is that given that it’s a competitive district, and Renzi is being investigated for crooked land deals, campaign law violations, and a significant roll in the US attorney firings, he though that it was time to get out of dodge.
On the brighter side, unlike some other people who have returned to private life *cough* Gonzalez *cough* Rumsfeld *cough* Bremer *cough*, he won’t have to worry about being hauled off to the Hague.