New Orleans was the major city. It will be the site of the major influx of federal funding post-Katrina.
Presumably the Gov. gets first crack at the graft statewide ... that leaves New Orleans for its mayor, perhaps ... Just a theory ....
Also, John Breaux, who has always cast himself as a "centrist" is tailor made to run for Governor. Breaux "trained" under the slickest governor of all time. Edwin W. Edwards. [Breaux was EWE's congressional aide before EWE ran for governor.] Breaux then went on to serve as congressman and senator. Mitch Landrieu does not have the statewide support or following that Breaux could snap his fingers and command. Landrieu could, presumably, pull together the old Landrieu crowd in New Orleans where his father served as Mayor. [I believe Moon left office in 1978].
I think this all boils down to whose power base is where.
"Goes from Lt. Governor to Mayor"
George Voinovich did the same thing in Ohio in the late '70s when he was elected Lieutenant-Governor with Jim Rhodes and quickly jumped in to run for Mayor of Cleveland. It ended up bolstering his chances of becoming Governor a dozen years later.