If you start at this undeniable fact then things start to fall into place...
We split the atom back in the 1940’s. After that we did almost nothing with it. We don’t use it for energy as much as we could. There has been a massive psychological operation to dissuade us from doing so. Who is responsible for that? Why did they do it?
We discovered an incredible new technology but then the powers that be, convinced us not to use it.
Why? Is it because it would have disrupted existing systems of power, wealth and influence?
How many other technologies have been discovered that they simply never shared with the public because they would be equally as disruptive?
How many people working on these new technologies would need to remain silent about them and not share them with the world?
The only way to do that would be to convince those people that they were the “good guys” for not telling anyone.
If you told them “This is alien technology so we can’t tell anyone about it or else it will cause mass hysteria. Now please get back to work helping us develop it.”...that is one way to solve that problem.
More likely to cause "mass hysterical laughter."
Read the manual:
https://cdn.preterhuman.net/texts/alien.ufo/SO-1%20Classified%20Army%20UFO%20Manual.pdf
This is how professionals keep secrets.