Public communication tends to occur within a more

Public communication tends to occur within a more formal structure, with set roles for speaker and audience.

Rules of turn-taking, setting and occasion make public address more organised than casual talk.

A complex structure is not the specific trait being named, since formality, not complexity, is the point.

A political structure narrows the idea to one arena, whereas public communication spans many settings.

A convenient structure is not a recognised descriptor of the public-communication setting.

Fixed norms and prepared roles are why public communication is called more formal.