I would submit an alternate hypothesis....
Let’s say the Manhattan Project never ended and continued as a government sponsored research project to develop new energy/military technology.
Let’s say they quickly discovered civilization altering technology.
Let’s say the powers that control the economy and the government, the energy industry, military industrial complex, banking industry, etc... would be negatively impacted by the disclosure of the new technology as it would destroy their levers of control.
How could you get the scientists and researchers to continue developing the tech while convincing them that it could never be disclosed to the public?....
You could tell them it is “alien technology” and to disclose the existence of aliens would cause “mass hysteria” and “societal breakdown”.
It is our technology and it is being hidden from us because our government hates us and doesn’t care about our well being.