An excuse is an apology that hired a lawyer.

An explanation attached to an apology quietly converts it into a defense. The other person came to hear that you understood what happened, and instead they receive a case for why it was reasonable, which leaves them holding the injury alone. Reasons can be true and still function as a way of conceding nothing.

Say the apology on its own and stop, even if the context is genuinely relevant. If the reason matters, offer it later, as a separate conversation, once the acknowledgment has landed. The pause between the two is what makes the first believable.