Why not "just" SMART on FHIR?

With SMART on FHIR included in the capabilities of every certified EHRs (today or soon), why is a (new) Health Cards project necessary? The SMART on FHIR OAuth model creates direct App::EHR connections, allowing trustworthy flow of data directly into an app. Why can't this be pressed into service for the Health Cards use case?

TL;DR—SMART on FHIR helps, but it can't solve the whole problem.

1. Equitability. Health Cards must work for consumers with or without access to a smartphone. The data in a Health Card must be interoperable, shareable, and tamper-proof even when the consumer holds records on paper.
2. Privacy. Health Card issuers shouldn't be aware of every verifier app and shouldn't be "in the loop" every time a Health Card is shared. (This would be a "user tracking" concern.)
3. Scale. Connecting every Health Card Issuer to every Health Card Verifier must not require 1:1 agreements or configuration. Furthermore, the Health Cards ecosystem must scale well beyond the realm of Certified EHR products.

(If you're paying close attention, you could try to address (2) and (3) by just... putting a huge amount of trust in a holder app—but it's unfair to ask/expect a consumer health app to provide this functionality, since it can't make guarantees.)