Why is it hard for men to apologize.?

My bf of 4 months and I got into an argument two nights ago. He started saying "i have nothing to lose". Then told himself to shut up cause it would just get things really heated and he would regret it. So yesterday I told him I was coming over to his house, and we went to a family dinner then went home and he was just absolutely wonderful to me. Treated me like a real princess. Why is it hard for men to apologize. I apologized but he has to.