Accountability for the information environment was built for a media system in which the publisher, the distributor and the accountable party were the same institution. That assumption no longer holds, and the structures built on it now reach only a fraction of the systems that determine what people see.
The framework question is narrow and answerable: how much does public discourse in a given jurisdiction depend on a given platform, how substitutable is that dependence, and can any of the platform's own claims about it be independently checked. Where the answer to the last is no, the opacity is the finding.