Why did the imperial family of Sui and Tang Dynasties become Xianbei people?

Basically, they all belong to Xianbei. After all, it was preceded by nearly 300 years of Wei, Jin, Southern and Northern Dynasties, especially during the Southern and Northern Dynasties, when ethnic minorities unified the north. The ancestors of the Sui and Tang royal families all came from this chaotic period of mixing between Hu and Han. , in time, the Sui and Tang Dynasties were founded successively. As far as the Tang Dynasty was concerned, Li Yuan’s mother’s surname was Dugu, and his wife’s surname was Dou. She itself had only a small amount of Han ancestry, and his son Li Shimin married the wife of Empress Changsun. This Dugu, Dou, The eldest grandsons all have Xianbei surnames. It can be imagined that the descendants of the royal family after Li Shimin are basically of ethnic minority descent, so it can be said that they are all Xianbei people