why does baba cry? how does this negate all we know about the social class traditions in Afghanistan? chapter 9

The next morning, Amir hid his wristwatch and a bundle of cash under Hassan's bed. Then he told Baba that Hassan had stolen from him. Baba called a meeting with Ali and Hassan in his office. When they arrived, their eyes were red from crying. Hassan lied and said that he had stolen Amir's wristwatch and money. Amir felt a pang of guilt because he understood that Hassan was sacrificing himself for him as usual. He also understood that Hassan knew everything about the night he was raped, that Amir stood by and did nothing to help him. To his shock, Baba forgave Hassan, but Ali and Hassan had already resolved to leave. From Ali's cold glance, Amir understood that Hassan had told him about the rape and about Amir's nonaction. Despite Baba's begging, Ali and Hassan left. When they were gone, Amir saw Baba cry for the first time. As though echoing Baba's grief, the skies opened up and it stormed during the dry season in Kabul. Baba was crying for two Hazaras which breaks the Afghan tradition of scorning them.