NFL teams will paint all their stands a team color to make it look like the stands are full.
Before pro wrestling got big matches were typically held in small arenas like the old Sunnyside Gardens in Queens or the Hesterly Armory in Tampa. Such places that had at most a 2000 seat capacity. The cameras were positioned in such a way to make these venues appear larger and more crowded than they actually were. I can see the NFL try and pull the same trick.