Because they are paid less than the value of their labor, and to much of the added value goes to those who are connected, including the CCP bureaucrats and connected capitalists. With free trade, rather than a government monopoly they would receive higher wages.
They are paid more than what they were ekeing out starving on their little plots of land.
It’s because they are willing to work for less than our entitled “labor force” with our minimum wages and benefits that they have been able to rise up so fast in the economic scale. And though they make less, things are much less expensive there. As a consequence, their PPP GDP is higher than ours, and as they’re productivity increases so do their wages. In fact it’s getting to the point that manufacturers are starting to move to Vietnam for cheaper labor.
Go to China and see the street packed with cars (including Mercedes Teslas, BMW, etc) , beautiful malls, restaurants filled with well dressed people, and ask them if their lives are better now than 20 years ago.