I remembered that my mother-in-law had been treating me badly over the past few years, and I rarely contacted her. Why do I regret calling me now that I shouldn’t have done this in the first place?

Your mother-in-law was not good to you a few years ago and you rarely contacted her. Now he calls you and says he regrets that he shouldn’t have done this. That means your mother-in-law has figured it out on his own or encountered something. When he meets someone, he makes a comparison and finds that you are still a good person. He thinks about what he did in the past and said, I'm sorry, you, he wants to improve you, and your relationship can give him a chance.