my first guess is because it make sense when you consider mountain chains

This is a plain valley area between mountains, bordering the nomadic tribes of the Mongolian plateau, because the traditional economic zones of ancient China are at low altitudes, and this is the main military stronghold of northwest China.

Topography of China

Arable land

漢武帝時期，漢朝疆域南至今越南北部，東北包括朝鮮半島大部，西部至天山。漢朝週邊還有許多少數民族建立的政權。

the farming civilizations

Terrain

Engagement bait farmer please stop stealing all these questions and pictures from r/geography .

the Huns robbed the chinese princess, that makes the Huns become Chinese. according to chinese logic.

Chinese never controlled Central Asia. These maps have nothing to do with reality.