This takes me by surprise too, though when one considers all of the money that can be made in lobbying, the decision by Lott to leave is less surprising. It is well known that he was a reluctant candidate in his last re-election effort and though he appears to have enjoyed his return to the leadership, lobbying seems to hold more allure.
I hope that Jon Kyl takes Lott's place. He is highly intelligent and deeply substantive and he is an excellent parliamentarian and inside player--precisely the kind of person who ought to be a Whip and perhaps, a future Leader for Senate Republicans. The other candidates to replace Lott don't appear to measure up.