There are five common explanations for this
But none manage to withstand any serious scrutiny.
To Control Information: In a similar way to 1984, control of information is control of everything. The flat earth is even mentioned in the book itself.
This would require a massive conspiracy traversing many different countries and empires over a very long period of time.
They are wrong: simply said, we are wrong about the shape of the earth, and there is no conspiracy. This describes why the earth might look round from far away: https://theflatearthsociety.org/home/index.php/blog/einsteins-relativity-proves-earth-flat
That post doesn't describe why a flat Earth might look round.
It is appealing to non-Euclidean geometry, and then trying to use a rule from Euclidean geometry in this non-Euclidean geometry where it doesn't apply.
It is quite over the top to think so many people could be wrong about the shape of Earth with all the evidence indicating Earth is round and none indicating Earth is flat.
To Maintain Legitimacy: During the Cold War we faked the moon landing. Shortly after they realized the reason they could not reach the moon was due to the flatness of the Earth. They were stuck in a lie, and had to continue it or lose legitimacy of our governments. Even today we would still hold onto this lie due to role Science plays in our ruling government.
Which is far too late.
People knew Earth was round long before the cold war. With the different governments fighting among each other, and even fighting themselves with different parties, it wouldn't be kept secret to protect the legitimacy, instead the lie would be exposed to show just how bad that party/government was. As for the role of science in government, do you mean like how the US government seems to like rejecting climate change and doesn't want to act on it? Science is not playing a large role in government. Also, if Earth was flat, then science would be showing that.
To hide the truth of the Bible.
This is the best reason I have seen. The problem is time. Earth was known to be round before the Bible was invented/compiled and the Bible has so many mistakes it isn't funny.
To Gain Power and Money: By siphoning off the space budgets and denying the world the resources of the Antarctic they gain a considerable amount of power and wealth.
But by doing it like they are, they would be wasting so much money it isn't funny. The less money they try to waste on faking space, the more people that need to be involved and the less money there is to siphon off for each person. The fewer people that know, the more money that needs to be wasted with people building things just to be destroyed. And then in addition, all the money spent on faking the data from space. You then have the issue of outsourcing. If it was all fake, why start paying commercial companies?
It is a very poor way of trying to siphon money.
It is much easier to siphon it from the military or top secret projects. With those, you don't need to provide anything to the public. No need to fabricate images of space, or provide magical GPS, just take the money and say people aren't allowed to know where it went.
So none of those excuses withstands scrutiny and the best one appeals to religious nonsense. A far better choice to keep the religion intact is to be like lord of the rings. Have Earth starting as flat, but then God changed it to stop the humans going to the undying lands. Alternatively, also have God intentionally make Earth appear round to test people's faith.
Except the argument makes no sense. Why would a tourist flight be concerned with their gas usage to the point of not actually visiting the one notable place on the continent. Pure malarkey.
Yes, pure malarkey. Why should they go over what you deem to be the most notable part?
A flight taking them quite far inland on a very hostile environment, just to see a piece of land which is in no way spectacular.