Why did Yang Jiajiang defend Dasong Jiangshan to the death?

Superstition says that Yang Jiacai was a "general with a hanging horn" in the Song Dynasty, and regime change was originally a matter for the Yang family. Whoever gives the lazy dragon an offering becomes the emperor. As a result, all the sacrifices at home were given to the lazy dragon, and the Yang family's sacrifices still reached the corner of the lazy dragon, so there was a saying of "hanging the horn general".