Cheap labor with little regard for workers and the working environment. There’s also political issues which we can’t discuss on this forum. Many of us have experienced poor quality. Household goods are just one example of the decline in quality which I have experienced. I’ve had my own issues with coach quality after manufacturing was moved to China. But to each his/her own. Buy whatever you love.
In any factory anywhere in the world, what the buyer is willing to pay is what they will get. Chinese factories are capable of exceptionally high quality production. If a buyer will only pay $10 per bag for labor, they will get $10 quality. Pay $50, you'll get $50, etc.
This is the rule with any factory including ones in the USA. That's how manufacturing works. Blame the brand and their desire for higher profits - don't blame the factory. The factory is only doing what it's been told to do.