Some polytheists knew the names of Abraham, Ishmael and Moses yet treated revelation to a human as implausible. They imagined that a messenger should lack ordinary human needs such as eating and drinking.
This wrongly assumes that being human and receiving divine revelation are mutually exclusive. A human messenger can remain human while carrying a message not derived from ordinary human knowledge.
Another question asked why every individual was not addressed directly. The response considers the possibility of revelation, the precedent of earlier messengers and divine wisdom in choosing the mode of communication.