International trade is not based on plain altruism. On both sides of the trade, some people benefit and some lose, but the net gains at both sides are positive. The article focuses on those hurt in US, but it does not mention how the US capitalists, consumers and workers not competing with China benefit.
> what is preventing the Chinese government to put heavy tariffs on those exports?
Chinese governments not only do not place tariffs on their exports, but also subsidies the exports. That is, the goods exported from China is cheaper than those sold directly in China. They do it for their own self interests.