The official website of the event announced in the requirements of entrants, which included not being resident in some countries including Iran. No explanation whatsoever was provided for the exclusion of entrants from these countries by the organizers.
“The Categories for entries are: (1) Travel Portraits; (2) Outdoor Scenes; (3) Sense of Place; and (4) Spontaneous Moments (the “Categories”). There is no limit on the number of entries per person.” National Geographic website states.
To support Iranian Photographers, Sing the Cause: https://www.causes.com/campaigns/93654-call-to-action-support-iranian-photographers