He's claiming a "back injury" which has been his injury of note since the Evans fight so one of two things happened.
1. Nog is yellow and cherry picking fights, he has no intention of competing and for all he knows he'll be cut if he loses so he's getting those massive checks for two more years.
2. The UFC is being shady they've locked up the big threats to Gustaf in other fights and they just used Nog to defraud Phil Davis, and Daniel Cormier.