The issue is that China does have a habit of selling things(Steel is a very good example) at such a low price that they don't make any profit on them, while simultaneously undercutting the competition so heavily that no one else can either, until all the competition is "starved out", this is of course market manipulation and an example of why a completely unregulated free market is fundamentally problematic. Some have been claiming Huawei is another example of this, that their tech is Chinese govt. funded, and sold undervalue so that Western companies have no chance to compete, but there's no evidence of that at the moment.
The labour aspect however, is entirely as a result of Western multinational companies wanting to ignore regulations & human rights to cut costs. The UK & US had cheap labour too, until we abolished slavery & started to introduce workers rights after the industrial revolution, so the higher in society quickly realised in order to maintain their levels of consumption they'd need some new people who had no workers rights, and thus sweat shops were born, rather than investment in automation or similar to solve the problems companies invested in a new world slave trade. Now China have developed, diversified their economy and established a growing "middle class", they're cracking down and have introduced stricter climate & pollution-based regulations(Over a third of China's pollution is actually directly attributable to Western consumption & companies) than most Western countries with workers rights coming quickly, big multi-national companies are starting to look elsewhere, Latin America in particular as more of Asia gets past their industrial revolutions, the cycle continues.
