Why are some people compelled to cheat at games?

Because they want to win without investing the time?

Think about it that way: why would anyone cheat in exams? After all not cheating means you would learn something which would in turn make nearly everything better in the long run for you.

The truth is, that some people just like to have the symbolic representation of success (good grades, good ranking in a game) without the actual meat (actually deserving it, because you mastered something). In school this might be more understandable, because people might feel like they didn't freely decide to spend their time like this anyways — so by cheating they minimize the time school takes from them (while rendering the time "lost" utterly useless).

It's only a game within the game. Outside the game is the metagame and social status as mentioned. I saying I read about some pro sports was if you're not cheating you're not trying hard enough. So it's considered an unstated rule in a sense.

i routinely cheat in single player games, i want to experience part of the story without the time investment.

i mean its my money, my time, who cares? I bought the game legit, i subscribe to "cheat" groups.. Does me getting to the last level deprive anyone else of that experience legit or otherwise? It would be different if i was posting spoilers day of release or something.