If you say God should give every single group or area a revelation, what stops you from extending that to every single person? I mean, if Moses has the greatest level of prophecy in human history, doesn't that leave us all out of something?

Obviously, we would not have free will if such a thing happened. If you look at the experience of the Jews at Sinai, you would notice that the Jews immediately performed an act that would seem to be a denial of that revelation. In fact, it is said that the moment they committed the sin of the golden calf is exactly the same moment when God handed the tablets of the law to Moses.

When the Jews are placed back into their normal existence after the Sinai experience, they obviously have free will. Other nations, such as Amalek, come to make war with the Jews because they oppose what has happened. Although Christians have distorted the concept, you need to recognize the real meaning of "faith". Faith is staying with something that you once new to be 100% true, even when you are outside of the experience that made you realize that. If every group on earth was given the same sort of revelaton, nobody would have freewill, but as it stands now, everyone does.