"While joining the Privacy Shield is voluntary, once an eligible organization makes the public commitment to comply with the Framework’s requirements, the commitment will become enforceable under U.S. law" from [1].

I'm not a lawyer, but it's fairly obvious that web services built in accordance with the jurisdiction of incorporation take precedence, especially when the software/service makes no customization to appeal to the EU. Maybe one runs a blog with content critical of China, but since they're running said blog as a US corp on US soil, China cannot apply it's laws on the said blog.

[1]: https://www.privacyshield.gov/Program-Overview