Think about the tons of research Janeway conducted, that was beyond anything any other starship captain could even dream of. The odds she beat with a skeleton crew and a bunch of partisans. She established an alliance with Species 8472, the worst enemy of the Borg, which are in turn the worst enemy of the Federation. In addition, she struck a critical blow to the Borg commanding a single vessel (a deep space ship designed primarily for scientific exploration).
I don't want to diminish Picard's accomplishments, but the Federation didn't even trust him enough to allow him to command their fittest ship into the confrontation with the Borg in the beginning of Star Trek VIII. Why would he prefer to work closer with those admirals if he could simply keep the captain's chair.
Janeway on the other hand had probably enough of deep space for a while after returning home, and it would seem more natural for her to accept a (well deserved) promotion.