Why not lie to gain a huge reward?

I think the basic issue is that this kind of question treats "reward" as a stolen concept. To call something a reward is to say that it represents a net gain to the actor. But how do you establish that something is a net gain? You can't look at it in isolation. Is eating a slice of cake a net gain to someone? It depends: Is he on a diet? Is he diabetic? Is it his birthday? Did he steal it? Etc.

To establish something as a reward requires seeing it in its full context, and its full context is your entire life. And that has a specific meaning. Rand's morality is not about collecting a bunch of goodies. It's about living a certain kind of life--a life that is all integrated around a certain conception of what your life is about. Think of Dagny. Her life is about running a railroad, loving Galt, being enthralled by Richard Halley's music--and these major values are also integrated. It would never even occur to her that something could be a value that didn't contribute to that sum. Money? It has value to her only insofar as it comes from and contributes to those central values.

To put it a bit differently, Objectivism's entire view of the nature of evil is that it is about inconsistency--the evil person is the one who does not pursue an integrated spectrum of values. He seeks "values" out of context, but that's like seeking knowledge out of context. What you gain is not knowledge, even if it looks like knowledge on the surface. Same with values. A person who "gains" ten or a million dollars at the price of inconsistency loses, because he gives up that which gives money (and any other value) its meaning.

Another way to put this point is: values are objective. Part of what that means is that for something to be a genuine value, it has to flow from a rational mental process. The person who discards virtue to gain an alleged value is saying, "To hell with that process." That is destructive. As Dr. Peikoff explains in OPAR, virtue is one. And by the same token, value is one. To make your values one requires integration. The "if I can get away with it" mentality throws all that out. That's why in reality "successful" criminals are miserable people who waste away their "winnings" within a very short period. The loo they get has no value to them because nothing has any value to them because they've rejected the precondition of valuing: rationality.