When someone says, "I am so sorry that I was not able to be there," they are expressing regret and apologizing for their inability to attend or be present at a specific event, gathering, or situation. This phrase implies that the person had a desire or an expectation to be there but, for some reason, could not fulfill that commitment or wish.
By apologizing, they are acknowledging that their absence may have caused disappointment, inconvenience, or a feeling of being let down in the other person or people involved. It shows that they are aware of the impact their absence may have had and that they genuinely feel remorseful about not being able to fulfill their obligation or be part of the situation.
The statement could refer to a wide range of scenarios, such as missing a social gathering, an important event, a supportive moment for a friend or family member, or even not being able to provide help or support when needed. Overall, it indicates that the person recognizes their absence and sincerely regrets not being able to be there when they were expected or wanted.