Becasue more and more browsers are limiting access to cookies not only depending on first-party context but also third-party context. So tracking users by web bugs becomes less reliable. By redirecting throught the domain, they can set and access cockies in a first-party context.
Great Wall, Geely and others have tried for many years. The problem isn't "stigma" but simply terrible test results for safety and quality. That's why most Chinese who can affort it buy Western or Japanese cars too.