The court reasoned sensibly: it's wrong to violate the rights of all citizens just to weed out a small group of violators. This is contrary to data protection regulations. The controversial Chat Control law follows the same logic: to find criminals, they propose monitoring everyone.
The problem is that any age verification system effectively becomes an identity verification system. And such tools rarely remain "just for kids"—they quickly become used for other purposes. The only secure way is to verify not the person's identity, but the device's status (for example, that it's a children's device). This is called age assurance: we confirm age without knowing who exactly is in front of us.