Because in case of prolonged injuries or layoffs their tournaments can continue to fixate on going after a title, whether interim or not.
To be fair, Bellator follows their tournament system pretty straight forward, so much like Pancrase had King of Pancrase Pro Tempore, an interim divisional champion makes some sort of sense.
I don't mind it. If the champ is out & can't defend then you allow another fighter to continue to climb. Then you can sell the fight as a unification fight & have an undisputed champion.
