Since time immemorial the world has been blessed by the gods. But over the centuries the populous received less blessings as time goes on. Soon it just stop. The gods were sad they were unable to reach to them anymore, but it was for an experiment; to see a world that have no need for gods. -- Anon Guest
The deities used to walk the earth with the mortals. This is known. It is there in the histories, it is there in the oldest tales. When the realms that made the world were closer to the core, before they drifted apart, and increasing effort was needed to walk between worlds.
There were times when supernatural forces could still influence the material world in observable ways, when those who worshipped, or possessed, by a power could do phenomenal things. Magic was real in those days of yore.
As a reality grows, more reality establishes itself. The power of the divine wanes. The influence of magic abates. Wizards were just wise. Witches were people who knew more about herbs and medicine than others. Warlocks and sorcerers were dangerously charismatic and manipulative. Clerics focussed more on spiritual wellness and less about medicine. Science explained things and the lapsing of belief made the walls between the Divine and the Mundane increasingly thicker.