Think about this: The Eye in Little Nightmares 1 & 2 is symbolizing the obvious. A nightmare. Except for the pain we make Six and Mono go through is just our vision of a regular nightmare, but for them, a never-ending loop of pain. But, the characters in-game are either awake (symbolizing the eye open) or sleeping (symbolizing us watching their nightmare through a screen). Since there are multiple of us playing, it will never end, even if there's an ending as in Mono becoming Thin Man and Six consuming the Lady's powers, we won't stop playing it. We're just seeing the same ending over and over again, even if you hack the game or give it a mod, the original ending is still there. The original ending always being there is causing the never-ending loop of the nightmare within Little Nightmares 1 & 2.