The flat earth "theory" is a means to control and seperation only. Its one of the oldest versions. Ancient philosiphers agued over this. Flat earth theory stems from the "Creation" idea. The gods made only this earth and we are in it. The other side is the argument. As we can see today that politics and religion are only a meens to control. Most things that are voted on, are not even close to being solutions to anything but someones bottom line.
Now the reason the "theory" continued after the great philosiphers figured more things out about our solar system, is this.
Keeping the world seperated, STILL.
During the time of the great sailors and explorers (conqurers) of the world, it was told that you had to be careful to not sail off the edge of the world. This places fear into people and therefore crushes dreams. The rich and powerful then own the oceans and they always have.
Do you follow me?