Apology Necessary

We all make mistakes. I (m40) screw up all the time and I make the effort to apologize nearly every time. So why is it, when my wife (f52) offends me, or causes a problem does she never apologize? The most recent occasion, she said something complaining about my mother which hurt me because I just explained to her how my brother is treating her disrespectfully. She knows she was wrong and the timing made it worse. The only time she apologizes is if I require it by asking. Even then it's like torture. I know she's sorry, she knows she's sorry, so what gives? I know from friends that this is very common. I'm looking for the perspective from women mostly but people in relationships with women, let's hear it.

TL:DR Why don't women apologize? Please explain your experience from either perspective.