Because the credential is unique. Imagine you submit it every time you log into Google, Facebook, and Youtube. They could all collude and see that the same age verification token was used and link the accounts.

Ok so you clearly didn't read the article because it calls out EUDI explicitly:

By the end of 2026, the 27 states within the European Union are expected to have infrastructure in place to do age verification within a "mini-wallet" app that will live inside the EUDI (European Digital Identity) Wallet. This is being met with plenty of warranted criticism from digital rights experts. The "mini-wallet" version is already being rolled out, with promises that the ZKPs are in working order. But recent insights show that the ZKP features aren't yet turned on except for the closed demo/prototype build (not the version of the app people are using “out of the box”), which the vast majority of everyday users can’t access.

Worse still, a security researcher found they could bypass the app's system using a quickly built Chrome extension that tricked the app into repeatedly accepting the same "over-18" token. It did so without ever asking for fresh verification.

Over 400 security researchers signed an open letter stating that age assurance checkpoints, even if implemented with privacy in mind, would cause more harm than good. A primary focus of their concern, which we share, is the fact that a centralized identity verification system creates a single point of failure that is extremely vulnerable to both cyberattack and authoritarian overreach.

Once the "mini-wallet" version of this is fully integrated into the EUDI Wallet, it will replicate these same failures, perhaps more, but at a much larger scale. At that point, the failures will involve many more pieces of sensitive information that the EUDI Wallet contains: passports, driver's licenses, travel information, financial information, to name a few.

the country is not trustworthy