There are many possible reasons. I’m not a flat-earther, by the way. But, I find it very interesting. So, one reason could be that the Earth is an infinite flat plane, and the elites don’t want us finding out that we can escape their control by leaving. Another is that globe-earth fits into a worldview system that reduces humanity to a random happening on a random rock flying through infinite nothingness with no destination or purpose (other ideas that flat-earthers would say are false - and a part of this worldview - would be things like abiogenesis, evolution, heliocentrism, and, for some, even atheism).

That’s a fine question but you probably never get a straight answer because no one really knows. The closest thing I can get is that whomever rules over us really just wants us to believe false nonsense about everything, even where we live. I’m not particularly religious, I do believe in God, but much of what we are told goes directly against what the “Bible” or teachings of Christianity say. Even the wearing of face masks is an example of this as the Bible says man should not cover his face.

The simplest answer is that we live under some kind of Truman Show style simulation that’s even more sinister than that as it is a Satanic inversion of the natural world.

By telling us Earth is a precarious and insignificant speck floating in space, it removes any significance of humans from a Creationist perspective. It opens up the door for other Satanic inversions such as Darwinian evolution, etc.

If you stumble upon a murder scene, you don’t need to know what the motive was to know a crime has been committed. Flat Earthers are usually intellectually honest enough to say “I don’t know” to certain questions like that one of yours, though everyone has an opinion about it.