True, and we weren't really shown what the whole city was doing. Rather we saw a representative portion. I am quite sure that there were people who didn't join the "fun." Rather, what we're told is that Gotham had a Warlord (Bane), and the idea is that, while the city was closed to exits, people could enter - with food, for example. It runs contrary to Bane's plan to just let the city collapse into utter anarchy, rather, he was there managing the chaos the whole time. What we didn't see happen, and I think was missing, was an effort of the citizens to go looking for the citizen with the detonator - a faction that believed his rhetoric in the stadium. Amidst the restructuring of Gotham's "government" the one thing that is lacking is the presence of a movement to figure out who controls the bomb - although I think you'd have to be pretty damn stupid to believe anybody but Bane or someone close to him had it.