Because there are buyers, both here and abroad.
Sorry to burst your bubble, Emperor Hongwu, but we're not the only people on the planet. Closing your eyes tight doesn't make reality go away.
You can ban all imports of inexpensive goods, and ensure that a big chunk of our wealth is pulled from economic development, etc., and put into higher priced toys, but that will just make us less competitive than others who don't do such things.
Do I like that? Nope. Neither do I like the fact that I can't fly unaided....but not liking something doesn't change the reality of it.
How about this...how about you boycott the stores and things will change, right? Oh...they won't?!? Well, then, why would America's boycott of these places change anything? Until it's a ban from all potential purchasers, the slave labor will continue.
And why stop at toys? What about parts for things we assemble? Wouldn't it be great if we had to raise the price on all of them, making any American product overpriced relative to other world competitors? Why, we could sit in our own little sandbox here, trading things back and forth at fake wages while the world passes us by. Oh joy.