Why did Zhu Yuanzhang first establish his grandson as king? Why didn't he pass on his position to his son according to tradition?

Zhu Biao, the eldest son of Zhu Yuanzhang, was originally made a prince, but Zhu Biao died in front of Zhu Yuanzhang. Zhu Yuanzhang also considered making Judy, the fourth son, a prince, but the minister objected, because Judy's younger brothers, Qin Wang and Wang Jin, were there at that time, and he wanted his eldest son to be a prince. Ma Huanghou, the wife of Zhu Yuanzhang, has no children, so in the order of age, Qin Wang and Wang Jin should be the first. But these two people can't afford the big responsibility. Later, Zhu Yuanzhang established Zhu Yunwen, the great-grandson of the emperor. However, before Zhu Yuanzhang died, his sons Qin Wang and Jin Wang also died one after another. But when the king of Jin died, two months before Zhu Yuanzhang's death, Zhu Yuanzhang had no energy to busy with the abolition of legislation, so it went away, and the introduction led to the change of Jing Nan.