What I mostly hear about Shein is their impact on the climate and how 'non-green' they are.
It's great. China does something faster, cheaper, and more effectively than us? They're bad for the environment. They're not sustainable. But have you considered the climate impact?
Greenwashing is so pervasive it's adopted in leftist circles as well, but it's an integral part of the imperialist toolkit.
edit: finished the video, the conclusion is basically it. shein didn't invent this system, they're just better at it. I remember IKEA being a famous example some 15 years ago, creating pressure on smaller suppliers because they negotiate for a very low price, but at least they're a reliable customer.