My guess is Vietnam’s spec was to achieve the same level of integrity as a paper document (ie. Minimal) and optimize for cheap/poor quality cameras.

Longer keylengths make it difficult to deliver sufficient payload in a QR. not sure about EU, but the SMART health passes that are the emerging standard use ES256 signatures.

The lack of global leadership for interoperable standards early on made this more difficult. You had the EU, Israel, US states and others who were ahead of the curve, but that approach had limits that were reached.

Now in the US we also have the issue of dealing with states with wacky political stances. States like California, New York and Louisiana, combined with private sector leaders like Walmart and Epic made SMART the defacto US standard, and other countries are recognizing them.