“Sorry” and “sorry, but” are two different words. The second one cancels the first.

An apology works by taking responsibility, so anything attached that shifts the blame removes the part doing the work. Adding a reason turns it into an explanation, and the other person hears the explanation instead. The urge to attach it comes from wanting to stay a good person, which is understandable and costs you the repair.

Try an apology with nothing on the end this week. Name what you did, say it was not all right, and stop talking. If context genuinely matters, offer it later, as its own conversation.