I refuse to speak for Cora. That’s his job. Not mine.
If you want me to speak for him, I will hypothesize that he doesn’t want to go to any pitcher on his staff - including starters, relievers, and openers - and tell them he doesn’t think they are capable and wants the front office to bring in a replacement ASAP.
Cora does interact with these pitchers. What if Bernardino likes his opener role? Think Cora wants to tell him “sorry, but I’d rather have Paul Blackburn out there and have you pitch less”?
The Sox do have a 10 man bullpen right now (if you count Pivetta as a reliever). The opener games are not as detrimental as they would have been 3 years ago when the Sox (like most teams) only had 7-8 pitchers in the bullpen…