US Winter Nationals

Having never swam competitively or trained for a big race, I was wondering if someone could explain to me why guys like Lochte and Kitajima layed big eggs at this meet. They were waaaaay below their world class times. Does it have to do with them not taking it too seriously or does it have to do with where they are in their training regimens at the moment. Maybe it is calculated? I just don't know a lot about this stuff.