I think it's more about the long term development of Bello. They want to keep him starting and give him the best chance to succeed. They also can't just DFA Kluber because it'll severely impact the Sox in the next FA class. Players aren't going to come here if they are just going to be DFA'd one month into the season.
The question is: how much value is there really to have an "innings eater" like Pivetta in the rotation? If the Sox want to win, they should have high ceiling guys, not the Pivettas of the world. They've also shot themselves in the dick over and over again by yo-yoing Whitlock and Houck in and out of the rotation and hindering their development. It just seems like their overall lack of the plan, or at least not sticking to one, has really impacted them whenever one thing goes wrong.
Their redundancies are injury prone players (Story, Arroyo, Mondesi, Paxton, Sale, Whitlock, etc.). That's not going to carry you through a season successfully.