Why was Hainan used as a place of exile in imperial China?

In imperial China, Hainan was utilized as a place of exile primarily because it was considered a remote frontier region on the fringe of the Chinese cultural sphere.1

During the Tang dynasty (618–907 CE) and beyond, the island remained largely under the control of indigenous Li peoples, while Chinese presence was restricted to small coastal settlements. Because of its isolation and the difficulty of maintaining effective government control, these settlements became a dreaded destination for criminals and officials who had fallen out of favor at the imperial court on the mainland.12

Despite its reputation as a place of banishment, the island eventually acquired an air of mystery and romance, partly due to the presence of prominent exiled figures such as the poet Su Shi, who contributed to the island's cultural history during his time there.1