The average income in the US is higher than the average income in Taiwan, Singapore, and there prosperous overseas Chinese communities. It is MUCH higher than the average income in mainland China, though surely there are many, many millionaires in Mainland China.
So far, buying wives seems to be more common in the US than most other places. There are cultural factors involved. There are few American wives in Kuwait, Qatar and the UAE, despite the enormous prosperity of those places. On the other hand, Rupert Murdock ditched his Aussie first wife for a younger Chinese woman. Senator Phil Gramm of Texas also has a younger Chinese wife.
Biden's mission to China was not to cause them to change their one-child policy. It was concerned with trade arrangements, and to give the Administration a chance to get acquainted with China's probable new leader.
Note that when Germans or French or British leaders come here, it is not to tell us that we have far too many people in jail in this country, considering our population, are really bad at preventing recidivism and should end the death penalty. In the same way, China's policy on population control is also not really any of the business of our leaders.