Jack, the way the software is set up that “space” can take whatever adverts are current so if someone pays for a full width banner ad the whole space will be taken up. If as at the moment the adverts are the less expensive smaller ones then space gets left at the sides.
I’m sure Kelsey would like to have full banner ads or a row of five smaller ones filling all these spaces but that is not always possible and it would cost more to keep changing the layout to suit current ads than what they provide in the way of income.