Didn't anyone ever warn you that deals with the devil don't work out the way you expect? If it were that easy to get what you want, it would be much more common practice.
Because people are forgetful and greedy.
You're making a lot of assumptions there which don't pan out in the real world: Absolute cooperation, absolute certainty, absolute accuracy. These things do not actually exist in the real world, which is why attempts to assert them on the large scale have always resulted in tragedy.