Why did the Sioux, the most profitable businessman on the ancient Silk Road, suddenly disappear?

When it comes to the Silk Road, we can't help but mention the Sogdians. The Sogdians are a famous commercial nation in the history of Central Asia. From the Eastern Han Dynasty to the Song Dynasty, especially in the Tang Dynasty, the Sogdians were the most active force in foreign commercial activities centered on the Silk Road.

The Sogdians are a world-famous commercial nation, and have established a huge commercial empire in East and Central Asia. During the Southern and Northern Dynasties and the Sui and Tang Dynasties, the Sogdians were the monopolists of the overland Silk Road trade and wandered around Central Asia and the Central Plains all the year round. The Book of the New Tang Dynasty once called them "where the interests lie". At the same time, they were also important messengers of cultural exchange on the Silk Road, which had a great or small impact on the culture they set foot in. Take the Tang Dynasty as an example. At that time, the popular dances of khufu, Huxuan and Lehu were mostly influenced by the Sogdians who settled here.

Then, as the most profitable businessman in the world in the Tang Dynasty, why did he gradually disappear, as if disappearing into the long river of history?