There is no one else for Demetrious Johnson to fight in his weight division. If anything this shouldn't be a flyweight match. DJ should go up in weight and fight for the bantamweight title. That makes more sense to me. He has no one else to face and he needs to go up and fight a different crop of fighters.
Also the latest word is that DJ is requesting that the fight be on a stacked card so that he can earn more on pay per view points. He said that if CM Punk can make 500k in his first fight and lose badly, then he should get paid that much as well.
Sounds fair to me.
I actually agree with you there man, It would be a lot more interesting if he went up a division.