Because the globe theory is the best there is. Namely:
1) it is not proven false
2) it explains pretty well what it is supposed to
3) it is relatively simple.
None of that screams unequivocal certainty to me.
Right. In the end, there are no unequivocal certainties in science. This is the difference between science and religion, and this is the main reason I usually try to avoid debating about science and religion at the same time.
I didn't say that the globe theory were right: I said that it is the best there is, and it surely better than the flat theory. But in the end, I cannot know for sure. We may live in a Matrix and cannot tell, because the Matrix itself prevents us from doing so, and within the Matrix the shape of the earth may be anything. I just don't believe that, because that theory is too complex, but I cannot prove it false.
My opinion is that the goal of any small powerful group aiming to take advantage of a much larger, but disadvantaged group is to make them feel small, or insignificant. You see it a lot in Soviet and Chinese architecture. To convince everyone that we are a happy little accident on a speck of dust in a Universe too vast to comprehend is really the ultimate realization of that. In the very least, it seeks to remove any empowerment one may gain in the knowing that he is a creature of divine origin, that is very literally a part of The Creator himself... whether or not you share this belief, you must admit it still must have an effect on the Psyche. If there is a power to be had with the true knowledge of our lower selves and our higher selves, then it would be advantageous to attempt to horde that knowledge, don't you agree?
Ok, I may agree.
So, let's assume that we have this small powerful group, that has an objective: to make people believe in theory X. Then, let's assume that this powerful group somehow, during their secret experiments, finds out that X is actually true.
Now, would that change the objective of the group? Hardly. Very few people lie just because of the joy of lying: lying is just a means to something else. If that something else can be accomplished without lying, all the better. So, the group would be all the more determined in their objective, that is to make people believe in X, and they would probably publish their experiments if that helped them to convince.
Shortly: even if a conspiracy existed, and even if it were proved that the conspiracy somehow profited from a certain belief, this alone would be no proof against that belief.