Steam is not paying taxes in Vietnam, and they have no official employee in Vietnam, that serves as a contact person. The latter is required by law. E.g. Shops need to have a shield on their front, giving contact information, and communicate clearly who's behind this shop (private person or company).
No, read that on r/steam from a vietnamese user, and it's my first-hand experience regarding Germany. Still, might be wrong.
But people tend to jump on South-east Asian (SEA)-countries, smelling suppression, and malintent, when often it's common law, even in western countries, but newly enforced in SEA countries