2. The Holder Gets More Over As a Threat
This is substantial to defending the briefcase. MITB wouldn’t be the title per say, but it would be treated like a championship which would give it more prestige and give the holder the perception of being feared. If the holder can hold off the rest of the locker room breathing down his neck than beating the champion is the final step.
WWE consistently books it’s MITB holder to lose, or be irrelevant for the surprise factor. The problem with that is that when MITB is successfully cashed in, the new champion looks weaker because they stole the title, or got lucky. If MITB was defended on a regular basis from constant threats and then cashed in successfully, the fans wouldn’t think he stole the title. They’d think he earned it.
He be worthy of being the champion, not a lucky guy who cashed in at the right moment.