Byrd: Why I Left the Klan
Because it wasn't politically popular anymore.
Byrdbrain is a man who is wholly unqualified to do anything in private life that would earn him the money, power, and perks he now enjoys as a Senator. Even with a Senate pension, he'd lose the perks and adulation common to that class. Thus, he will literally say and do anything at all to remain in his position, even things he absolutely doesn't believe in personally.
He is a reprehensible human being, and his continued presence in the Senate is a herpes sore for his home state, and the nation.