Look closely at the concentration of buildings, warehouses, skyscrappers, shipping containers, ect... Are you honestly going to say that there were more supplies across the bridge?
??? Those people weren't looking for "supplies" - - there were no "supplies" in Gretna. They wanted to cross the bridge in order to see what kinds of jewelry, stereo equipment, and silverware were left behind by the people who had evacuated Gretna.