Ex-girlfriend apologizes?

I dated this girl for a couple of months. She ended the relationship and although it was tough, I managed to move on. We barely, if at all, talked since the breakup (6 months ago). If I initiated contact, she will respond, but in a neutral, "being polite" tone. She did initiate contact with me once, but she reverted back to her old self the next day (neutral and "being polite"). After that, we didn't speak to each other for a few months.

One day, I get an email from her. It's fairly short, but it was the first contact from her in months. She told me that things had been changing for her in the past year (growing up as a person). She explained to me why she was being "hot and cold" in our relationship (she wasn't in the right head space at the time), and apologized for being like that during our relationship. For the first time ever, she talked about how she treasures the times we shared together. And that was it. I responded in a happy but neutral tone. I told her not to apologize, since I said that the breakup was the right thing to do.

The thing that puzzles me greatly is why did she apologize like that? Why tell me that she's been growing up and took responsibility for the downfall of our relationship? Why not apologize for being distant during the post-breakup months? I mean, yeah she knew I wasn't happy about the breakup, but she knows I'm doing good in life. Oh and get this, a few days after I replied to her apology, she got a new boyfriend (she didn't date anyone since we broke up 6 months ago). She hasn't told me she's seeing someone but I heard it from a mutual friend.
Ex-girlfriend apologizes?
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