Your statement is pretty glib. The election was on November 4, 2008, the inauguration was held on January 20, 2009, that's a time span of two months and sixteen days. That's plenty of time for people to make plans for transportation to Washington D.C., as well as time to find and reserve accommodations.
How much time do you think the citizenry of New Orleans, population about 450,000 before the storm, had to secure their property, pack up their belongings, try to find a hotel room within a reasonable radius (not easily done), and head out in the hopes that when they return they still have something to return to? Add to that dealing with bumper to bumper traffic that turns a six hour trip into a twenty hour trip and you have a vague idea of the ridiculousness of your post. Also keep in mind that despite the never ending slams that people did not leave, 80% of the population evacuated before Katrina came through. That means that the people you saw on CNN and FOX in September of 2005 constitute only about the remaining 20%. Some of those people didn't leave because they didn't have have the financial means to secure a place to stay, or a way of getting there. As one whose family has evacuated several times, the last being for Gustave, I can tell you that with gasoline, food, and lodgings etc, it's not a cheap endeavor.
These pictures are a good illustration of the evacuating before Katrina. That's Xavier University of New Orleans in the background of the first one and the Superdome in the background of the second.