New theories are usually false. The theory that the world is a ball is new compared with the old and original fact that it is flat. So you have added your new theory along with the theory that the earth is a globe.
Actually, older theories are more often false because the people who've created them lack sufficient equipment to really determine it.
When time passes, theories are overthought again and again, equipment that can give us facts gets developed and old theories are replaced by newer, better ones.
Also, I don't see how you can say "the old and original fact that it is flat".
These theories came into life even before the year 200.
People didn't have any equipment but their brains.
New equipment makes us able to determine things better and more accurate.
In the olden times, it didn't make sense to why it would be round.
With the current equipment, we can explain a lot more things.
And there is no reason why the government would keep the fact that the earth would be flat hidden from public.
In many countries, the governments are chosen by the people themselves.