One of the explicit design choices in this was to limit people's tendency to screw up apologies in the heated moments when they haven't yet internalized the outside world's perspective of their message. I'm glad you brought up the searching of how to apologize - it's one of those super important life skills that we haven't done a good job of teaching people about. We have to design with this constraint in mind.

One of the things I think about most in design, especially in design of social products, is limiting self-sabotage. This is because there's really significant emotional risk in social systems of feelings like being exposed, misunderstood, etc.

This is why I favored the approach of not including a Follow-up or further explanations. It makes the choice Mea Culpa very simple, favoring cooling off of conflict over continued debate. Basically people can go back in their corners and think about things, and figure out how to approach things again later if they choose. It is an intentional choice to favor respectful debate over maximal information exchange, acknowledging the medium's tendency to escalate conflict and the presence of many bad faith actors.

Also note this feature does not take the place of the apologies you're talking about, it just offers an acknowledgment of mistake and an opportunity to forgive.