Back when Zhou Tian opted to enter the Divine Realm, he discarded the affection he held for the Beastman Tribe in his heart, and after a quick examination of the dubious information about the Divine Realm, he unleashed his power and flew towards a certain domain in the Main Plane.
As many novels depict, the world Zhou Tian inhabited was immensely vast, with every continent significantly larger than Earth. By that measure alone, Zhou Tian's world was certainly superior to the world of Earth.
Yet, when it came to the Divine Realm he was heading towards, his highly advanced world was still considered a Lower World.
Just as Earth is one amongst countless planets in the universe, no matter how vast Zhou Tian's world was, to the Divine Realm it was merely an inconspicuous domain among millions of Lower Realms.
