I don't understand the motivation behind all the cover up if the earth is really flat. Why would they spend all those resources to deceive all of us, what can they gain from the lie?
Well firstly it is not secret the earth is not a sphere, and the spherical and heliocentric models are never actually confirmed, but then they are not denied either. Thus it is no conspiracy, for a conspiracy must be secret.
As for why all the effort, there is a long list of why they would do such. I suppose that in truth they actually gain nothing since they cannot actually change reality. Though what they have with this is the ability to manipulate people's minds. The foremost reason seems to me to be to try to deny the Bible and support paganism or heresies, which is at the root of the origin of the heliocentric and spherical earth heresies.
In more modern times this stuff has its origin in the Cold War, so as to create an illusion of technological, economic, and militaristic superiority. This is where the purpose of the illusions has shifted from an outright denial of the Bible to being used as a tool of mind manipulation. Basically, it is a propaganda campaign. Even at the very start of the so-called Space Race it was known and published to be a propaganda campaign, thus it is again not secret nor is it a conspiracy.
https://www.youtube.com/watch?v=KMFvr1VwSSo
[video=youtube;KMFvr1VwSSo]https://www.youtube.com/watch?v=KMFvr1VwSSo[/video]
In the post-Cold War era the reasons would be to continue to maintain the illusion of American superiority and also to continue the propaganda machine turning. It's really very simple and standard propaganda all around. What we are seeing emerge in this time is space propaganda has come full circle, with the Cold War over and the need to make up elaborate hoaxes no longer needed, the space propaganda has once more returned to its pagan roots. In our time now it is being used to prop up false religions in the West (ie: naturalism, darwinism, ufo cults, aliens, etc.)
In summary, they have been lying so long it's easier in their minds to try to maintain such absurd lies rather than to risk embarassment of admitting the Bible is right and man's science falsely so-called is wrong. Ironically of course though it is not easier at all, but they have to keep piling on even more absurd lies and false wonders to try to prop up their lie, which only makes their lies even more easy to detect. If it were to be admitted to be a lie various governments and factions would lose a significant amount of secular power and mental control of people. It doesn't matter though, like all lies, it cannot last forever.