This is because he came without the Ideya of Courage, and has yet to find his own Ideya of Courage. After all, he sends all of his creations and dreamed-up people to get things for him, and you only need to hit him, what, three times in the game? Because of that, he has stayed locked in the Night Dimension for years and years, perhaps even defying the laws of physics and aging and being Really 700 Years Old (I read somewhere that sleep slows the aging process by a significant amount, though that might be debatable). He's been stealing Ideya from other Visitors as compensation for his lack of a Red Courage Ideya, yet ironically, the Red Ideya is the only Ideya he cannot steal, nor keep.
So he goes on, creating more and more Nightmarens and becoming the God of Nightmare. For years he has been trying to get a Red Ideya, but has failed so often — so very, very often — that over time he has completely forgotten what he had initially set out for. He loses himself, going crazy to try and get at his Red Ideya, that he leaves his waken life completely, even forgetting that he is a Visitor. This causes problems for his 'Real Life' body, which is still asleep. While the Wizeman of the Night Dimension goes on a reign of terror and malice, in a desperate attempt to finally get his blasted Ideya, the Wizeman of the Real World is still a child, doodling designs for Nightmaren and the faces of other Visitors, but only as a subconscious reflex. In fact, Wizeman has become convinced that getting a Red Ideya will wake him, forgetting that it is of his own free will that he awakens.
Whatever little boy Wizeman may have once been has been lost, leaving behind a broken child in the Real World and a heartless overlord in the Night Dimension.
- Wizeman being a Visitor was confirmed in his backstory in the original.
- I think he DID fall into the Black Sea. Dualization with a Nightmaren extends the time limit before Awaker-ghost-thingies, giant alarm clocks, and Night Over screens will force you to wake up. Falling into the Black Sea gives you an endless nightmare and a coma. Connect the dots.
- Interestingly, the red jewel on NiGHTS' chest is supposed to be part of a Red Ideya that attached there. Building upon the above WMG, that may be WIZEMAN'S Red Ideya.
- Also, NiGHTS helped at least 4 people find Ideya; judging by what NiGHTS is, perhaps Dualization temporarily shared those Ideya with him?
2nd and 3rd level Nightmarens were humans that lost their souls, and consume Nightopia, Nightopians, and hunt ideya mindlessly because they're desperate to be whole. They might have not even been bad people originally, so much as completely devoid of ideya; the parts that make up their soul. While 2nd and 3rd levels would have lived a broken afterlife without Wizeman anyway, 1st levels have complete souls, and would have been destined for Nightopia without Wizeman's intervention.
Reala's will got broken and he lost faith in goodness, NiGHTS didn't, perhaps because he got a lucky escape, or perhaps because he has the stronger will.