It said by some who know him he hates being senator. He prefers a executive political position. It better suits his personality.
The announce his intention to retire from the Senate. I don't think he has a snowball's chance of being elected governor again, but if he really hates being a senator...
Maybe he’s thinking of a presidential run in 2024.
He positions himself as a moderate democrat (a la Bill Clinton) against the radical Harris. He positions himself as reaching across the aisle bi-partisan with standing up for the fillibuster, etc.
He could have a chance at being president.
Hell, if Bill Clinton could be president.....