The IWC seems intent on finding a boogeyman behind Corbin losing the MITB briefcase, but can't it be just a wrestling angle? He's not the 1st to fail to win the title when cashing in the briefcase. Cena distracting him and costing him the world title actually gave their summerslam match a purpose or some heat. Ratings have been low after Wrestlemania so the failed cash in gave the episode of smackdown excitement and an unexpected ending. Jinder's heel title reign is going better than expected so having a heel with the briefcase isn't needed. He's competing for the US title, why would he care to do so if he could fight for the world title? And if they want to put the world title in Corbin, there are plenty of PPV events to just give him a match.
Yeah, but it wasn't an angle as intended, though. The original booking was Corbin cashing in at Summerslam and beating Nakamura, and it was literally changed the night of that Smackdown to having Corbin lose the briefcase. Even if Jinder's title reign is "better than expected" they didn't have to immediately take the briefcase off the table and job out Corbin. The whole thing was just a waste of everyone's time.