Think about it... U.S. congress can't agree on anything anymore. The Middle East is still is huge conflict, with hardly any discernible governments to speak of. Many African countries have either shadow governments, or no governments at all. Many of the ones that are there are highly militaristic, and not welcoming to foreign relations. There are also an innumerable amount of countries that hate each other, often times for really no reason.
So with all this in mind, how can we expect ALL of the world governments to collude on this one thing, without any real benefits from it? This would require them to all have the same facts, same examples, same experiment results, same everything. Just from a logistical standpoint, this would be pretty much impossible. What if somebody stepped out of line and spoke up about the earth being flat? That would bring the whole thing crashing down, especially in today's world where information spreads so quickly and easily. If there were any scientists who really believed in a flat earth, who had concrete evidence supporting their claim, they would have already spoken out.
If the world was indeed flat, why wouldn't some rogue government just blow the top on everything and ruin the whole deal? Say for instance, North Korea decided to reveal with solid backing evidence that the world was flat. The credibility of every other nation would be ruined. How would the U.S. citizens feel about their government if it was suddenly revealed that their whole life was a lie? Thankfully, we will never know, because no such evidence exists.
Honestly, this is the biggest gap in logic (Other than the blatant disregard of physical evidence) that plagues the Flat-earth society.