The higher ups (shadow governments) have acknowledged alien existence on Earth, and hide it to prevent the collapse of society.

To start, when I refer to higher ups/shadow government, I’ll use the USA as the main example but it relates to any powerful country. The top brass of the military or agencies like the CIA come to realize early on during/after the World Wars that you can’t trust the elected governments with information and how to properly handle/use it. So the brains of military and CIA went behind the governments back to create a very select group of people to handle information and make decisions. Those select people took it upon themselves to study in secrecy phenomenon they encountered, and only self appointed their successors. These were lifetime appointments, and only a very few people were selected to be a part of this secret upper echelon, that took it upon themselves to study and react to events outside our understanding. They don’t care to meddle in the affairs of society as what they deal with is not even in the thought process of the population or governments. They don’t care about who is the president or head of an agency, let the people have their pick through elections or such. Let people have the sense of freedom. At the end of the day, the head of state is a temporary employee, while they work above them without their knowledge. Why share secrets to the president who at most will be in charge for 8 years or Secretary of Defense when they can destroy your work and progress has spanned decades if not a century. The president or head of agencies are not even aware that this group exists above them. And these secret groups from different countries keep some form communication and share information with each other even though in normal life those countries are against each other (ex. USA/UK vs Russia/China). They all work together to understand what is actually going on when it seems like an existential threat, but also keep secrets in their own best interest as in reverse engineering for military power.

The reason why these very small, selective, secret groups of people haven’t made their presence know or come forward with their knowledge, tell the truth, or asked governments and the public to help aid them; is that they understand the their knowledge would make society come crashing down. As of now, the overall human population conforms to certain rules, mainly because of religion. Even if you’re atheist, the foundation of rule in the world you live in is built on beliefs of our ancestors that there is a god(s), and the messengers taught us what was the right way to live. Even though there is turmoil in the world, the billions of people on earth still have a framework from religion that keeps some sort of control. But if these groups of people came out and said that extraterrestrial beings have been among us and we’ve been tracking and studying them, the notion of god (in most beliefs like Abrahamic religions) seizes to exist. The rules of society collapse as it was all imaginary, and people find out everything they believed in is false. Humans have shown over and over through history to be self destructive. So to keep the world in tact, these secret groups keep studying the advanced beings among us, but can never let us know what they actually know. At least not yet.