Because it’s not an apology. It’s not an admission of guilt. It’s not even sympathetic in any conceivable way.
It’s just pushing the blame and the guilt off your shoulders because you, quite literally, do not give a flying fuck about the other person.
It’s not kind and it’s not polite. It’s not a nice thing to say at all. When that’s all you have to say, it’s demeaning, and it sucks. Better not to have said anything at all.