Why do exes wait so long to “realize” how badly they did you in the past?

An ex of mines from 5 years ago broke up with me and left me for another woman 4 years ago. At the time it really hurt me. I cried for days and questioned if it was me. If it was my looks. If I wasn’t good enough when it came to sex considering he was the one I lost all my first to. It was also the way he exited the relationship. He told me that he and I were done and to never call or text him again. The hurt lasted for a year. Throughout that year he would come back and message me, even though he was still with the girl he left me for, but only for sex but he made me believe it was for more than sex because he knew my feelings for him were still strong at the time so any conversation from him after he had dumped me felt great to me at that time and that only hurt me worse to know once again he was using me and not treating me right. That’s when I knew I needed to move on. For the past three years I’ve been great. Even experienced dating again. I haven’t thought twice about my ex. Randomly a few days ago I got a request on Facebook from what seemed to be a fake page. The page requested to message me on messenger and after reading it I knew it was him. He was asking how I was, he went on and on about how wrong he was for what he did to me and that he should have appreciated me more and not had used me the way that he did because I didn’t deserve that. He even started sending old Snapchat’s of us, that to my surprise, he still had and my reaction to it now vs how it would have been three years ago when I still felt strongly about him told a lot about how true the saying “The tables always turn.” Is because I remember when he left me, I just wouldn’t accept it and kept messaging pictures, snaps, messages etc of us to make him feel different about his decision but all he did was blow me off, now he’s doing the same thing and feeling regret years later. I don’t want to be mean but I really don’t want anything to do with him.
Why do exes wait so long to “realize” how badly they did you in the past?
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