Since Han and Tibet are of the same origin-why did our ancestors go to Tibet?

The Qiang tribe entered the plateau very late, not the Yanhuang tribe moved eastward and westward at the same time.

After the Eastern Zhou Dynasty, especially after the Spring and Autumn Period and the Warring States Period, due to the increasing pressure from the Central Plains, it was forced to move westward. After the Qin and Han Dynasties, more people fled to the plateau, because the Han people gradually consolidated the Central Plains and expanded around. It has been 400 years since the Han Dynasty suppressed the rebellion of the Qiang people. Qiang people either migrated to Yunnan and Southeast Asia, or fled to the Qinghai-Tibet Plateau with harsh environment. It is out of the question.