Because a modern wifi router requires a minimum of 6 antennas. 9 is even better.
This lends itself to a spider like design with just a ton of antennas sticking out of a box, or a trash can with the antennas hidden inside around the outside edge.
Do you have other ideas for how to lay it out?
My radio knowledge is not up to par, but couldn't a phased array antenna setup allow for friendlier form factors?