Why do so few former governors run for their old job? The law bans consecutive terms; it doesn't stop them from running again later.
Taking a look at the recent Governors...
1. Chuck Robb took the Senate seat and was then considered as possible candidate for national office. No point of returning to the Governor's Mansion
2. Gerald L. Baliles... now he was a likely candidate to do so, considering that two Senate seats were locked and that he did not purse, despite some speculations, 1992 Democratic presidential nomination. Yet, he abandoned active politics after his term ended.
3. Douglas Wilder. Briefly attempted to run for Senate as indy in 1994. Probably wouldn't be able to become Governor again even if he wanted.
4. George Allen. Yes, we all know his story. Preferred to take the Senate seat, especially since he was a possible national candidates as well... until he had his Macaca moment.
5. Jim Gillmore... Remember that loser? HAHAHAHAHAHA!
6. Mark Warner, already discussed here.
7. Tim Kaine: again the Senate is better.