tl;dr Once the U.S. listing is successful, the investor's return is in U.S. dollars. If funds return to China, they will enjoy various preferential treatments for overseas capital. Of course, it is also possible not to return to China and to be divided among the bigwigs hidden in investment institutions. Therefore, overseas listing for cash is an important way of capital outflow.

Incidently, the recent bitcoin shutdown by the Chinese government is also partly due to capital outflow concerns