7.2 Why not make app stores or devices do all age checks instead?

Device level and app–store approaches can help in some contexts, especially where a user wants a reusable age proof set up once, and several US states are legislating in this direction. But they are not a complete substitute for service level accountability. Many risks arise inside websites, apps and accounts after installation, on shared or second–hand devices, and on the open web that app stores never touch. A good system allows privacy preserving reuse of age proofs, whether from a device, a wallet or a provider for lower risk use-cases, while keeping clear duties on the service that create or distribute higher risks. The two models are complements, not rivals, serving different use-cases.