There's always an incentive to cheat: economic, reputational… people cheat in single-player video games. People cheat in sudoku puzzles. By removing all incentives, all you do is destroy the concept of "cheating", not prevent the behaviour.
I think you've listed several disparate incentives that should be looked at separately.
Economic incentives are what this thread is about. If those are removed, some instances of cheating will subside.
Reputational incentives are similar and harder to address, but they are also less strong because the cheating has a much higher chance to backfire. If you are found out, your economic benefits might continue, but your reputation is immediately damaged.
Singleplayer games are an entirely different situation. There's clearly no economic incentive here, and reputational incentive only applies if you are looking to share your singleplayer result with other people, in which case I could argue it's no longer singleplayer in the game theoretic sense. If it's not that, the only remaining motivation to cheat at something like Sudoku or a singleplayer videogame is to learn or at least satisfy an itch or curiosity, which I think is a perfectly legitimate motivation.
