I am sorry does not heal the wound.
It does not solve the problem, it does not undo what was done, it does not wipe out an unpleasant memory.
I am sorry is not a wand to wave at distressing situations. It does not draw a plan for the future and it does not promise it will not happen again. It does not go any farther than you want it to go. It often does not fill the gap. Very rarely it changes the narrative. And it never is the end to a conversation.
I am sorry does not do any of the above.
Yet without I am sorry none of the above can ever happen.
I am sorry is the essential stepping stone to what comes next in any kind of relationship.
What actually is next depends on you.