There are many regions/nations that are either hostile to the current international order or ungoverned. There is no chance of such a global conspiracy working

There are many regions/nations that are either hostile to the current international order or ungoverned. There is no chance of such a global conspiracy working for many decades to cover this up. Besides, just think what hostile countries would do to get access to alien technology or just prevent their enemies from it. That would be very, very noticeable. We would have tons of https://en.wikipedia.org/wiki/Project_Azorian https://en.wikipedia.org/wiki/Project_Azorian all over the world.