The peoples who say that there is slave labor in china, let alone that it is commonly used by corporations there have never provided evidences of such a thing as far as I am aware. If you think there is slave labor in china you need to prove that.

As for the lack of environnemental regulations, I don't know chinese law enouth to deny it with full confidence but given the tremendous governmental effort in green tech that has made them wold leader in renewable, electric cars and more I find that unlikely to be the case.

The explaination is more simply that chinese labor is way cheaper than western labor while at the same time way more industialized than other places with cheap labor like india and has also fully or almost fully integrated supply chains that make production as a whole cheaper.

As for IP law, again I don't know enought of chinese law to say exactly how it works but they have indeed no reason to follow western IP laws.