I think Charles was/is expecting the team to tell the outgoing driver to cool off and let him be the clear #1 for the rest of this season. Carlos just isn't going to do that.
He plays the team game when it suits him but he and his family are well versed in the politics of motorsport. Carlos knows surrendering to Charles at this point serves no purpose.
More spicy overtakes are coming, from both drivers.
If they wanted a complaisant second driver willing to follow team orders, maybe don't start with telling that driver he's gone at the beginning of the season? Why should Sainz yield to Leclerc, he needs to stay performing and ensure he's impressing other potential teams.
And honestly with how the musical chairs are looking, it's totally possible he'll finish 3 or 4 in championship and still miss out on a seat next year.
Obviously not to a STFU moment. But, that moment will come if he causes grief inside the team. He knows this and the rumor is he'll have an announcement soon, so maybe he doesn't care.
Without Carlos driving at his peak, Ferrari will not be able to guarantee second in constructors let alone challenge for first as perez continues to contribute nada to red bull. I'd imagine they'd like to continue to be second and specifically ahead of maclaren. To do that they'll need him to be motivated to be a driver and I don't know much about him but if I've seen anything from the races, it's that he's motivated by personal achievements.
Either way double Ferrari dnf from infighting entertains me greatly. :)