Despite The One's great power, The One still has an almost human-level attention like the other gods. This means that precious few who worship The One ever have a chance to see their god. Indeed, in the current day, The One hasn't spoken to anyone for decades. None of the Chosen are sure why, and it's of constant concern among the most faithful. No prayers are answered, no miracles performed. Indeed, the historical record shows no other time period even as long as one year without The One's direct contact - depending on who you ask, the modern-day dry spell is either deeply concerning or greatly relieving. I have interviewed many - members of The Chosen, other Freemen and religious figures, and even commoners. The theories for The One's absence are numerous, but a handful of them appear to be reoccurring.
Many of the Chosen say it's a matter of a lack of faith - The One is off creating new life on another world, tired of the war and greed of humanity. This opinion, of course, is completely impossible to prove or disprove, so I leave it here only that the reader may form their own opinion.
Conversely, many priests of the other gods believe that The One has stepped back to allow The One's children (the greater and lesser gods) to take more ownership of Verden. It's akin to a parent stepping away from their grown children, letting them chart their own courses. As the above, I am unable to find any evidence proving or disproving this theory.
Some of the more open-minded citizens believe that The One is focusing more on the magical beings of Verden - elves, dwarves, and the like. It is certainly a question as to why the gods seem to have forsaken those groups in the past 2000 years, focusing on humans instead. Perhaps a reversal of sorts is incoming. However, I have found no evidence to show this is true, at least not from dwarves and elves I have interviewed in Taelmoor.
The more paranoid and violent citizens believe that there is a secret war in heaven, where another god or gods is trying to subvert and steal The One's power. While a bit alarmist, this theory actually holds some amount of water. Some of the Greater Gods have also withdrawn from human society to varying degrees - Zeale, for example, hasn't been seen in decades either, Morum has taken to responding only extremely rarely, and Habeth has explicitly stated he will no longer grant miracles. Certainly, something is going on.
Last and simplest, many believe that The One has simply fallen asleep. Given that there is no historical evidence this has ever happened before, I find this theory particularly unlikely. However, who's to say what the sleeping cycle of a god looks like? Perhaps a day to a god is thousands of years. I shudder to think how long the night would be in that case…
In the matter of The One's disappearance, the only thing that is clear is that we will not know why until The One comes back and tells us.