Why did trade along the silk road flourish during the time of Han Kushan Parthian amd Roman empires?

Sik road was the name of a network of trade routes which connected China and India to the eastern Mediterranean and Europe. The main item of trade was silk from China, which was a highly sought after luxury good in the Middle East and in Europe and made China rich. China imported dates, saffron powder and pistachio nuts from Persia; frankincense, aloes and myrrh from Somalia; sandalwood from India; glass bottles from Egypt. Sp[ices and other luxury good also traveled to Europe through these roads.