But then as Foy points out, the French army as a whole at that time was not really up to the task.
Mostly ad-hoc units, the scrapings of the depots. My guess is most of them had been left behind in the depots for good reason. Dupont had been an excellent division CO with valiant duty to his credit. But independent command in a strange land in arms against him put him at his level of incompetence. He was burdened with loot and perhaps suffering from dysentery.
It reminds me of the Moors retreating with loot when they were caught at Tours. Except their escape route wasn't cut.
Regarding French looting in Spain: I once went to an exhibit at the NY Metropolitan Museum of Art on Spanish paintings that influenced French painting. A truly amazing chunk of the large exhibit featured the paintings looted by Marshal Soult. He must have had quite a wagon train just for them. He also had a good eye, might have made a better curator than a general.