How China built ‘iPhone city’ with billions in perks for Apple’s partner

Beyond iPhone in China, I have a larger question. Let's say I were building product in the US with child labor in unsafe conditions not adhering to US laws and regulations. Would I be allowed to sell that product in the US? Probably not. If I were doing similarly around the world then seeking to sell that product in the US, it happens to be the case that I could.

Why is that the case? Why is it that product built in foreign countries that do not adhere to US laws and regulations on manufacturing and labor are allowed to be sold in the US?