I've said this before, The P4P rankings are a big factor. Just look at the two biggest draws in boxing. PFB and PAC. Why because common folk don't know who the champions are as they are ranked in the multiple sanctioning bodies.

People turnout to watch the playoffs, the Superbowl and the World cup. When the champ is fighting, people show up. In this boxing era, the reigning "Heavyweight Champion of the World is Floyd Mayweather and Manny Pacquiao" i.e. people understand the Champion on top of the P4P list.