Because she wants to appear profane, i.e. common. That way the family representing America sends the message to the world that America is profane. Nothing special about the family in the White Hut... no, they are just clueless slobs, and that's the way it is supposed to be. Yeah, why bother to look dignified. That would be a glorification of a people and a system that is just so yesterday. Full of white racist dead men's bones and all that.
I think you’re right, because it takes effort too look as bad as the Obamas do. I go to Walmart better dressed than that.