Because of Juppé's condemnation in court, he wasn't a rival for Sarkozy anymore.
OTOH, Fillon the PM might be happy to be rid of a man as important as he is. Un roi sans divertissement est un homme plein de misères
He could have done that also to follow the more to keep friends close, enemies closer... *Lunatic*, n. One whose delusions are out of fashion.