Allegedly to avoid alarming the public and creating financial anarchy.
And the secrecy itself became a bargaining chip with the ETs. Our agreeing to the cover-up allowed them to carry out most of their nefarious operations away from the prying eyes of the press. In return for our collusion in keeping it all under wraps, they granted concessions that we probably could not have gotten otherwise, as we raced feverishly to catch up with the technologies that were thousands of years in advance of our own.
Unfortunately, we paid a heavy price for this agreement, since we lost the advantage of opening up the scientific problems to the best minds on the planet and instead relied only on scientists with a military affiliation who had to confine their research to strictly military objectives…..
and were not free to explore ideas for technology that would benefit humanity.
in fact, in the early days, many of them were ex-Nazis brought to America under operation paperclip who liked to work with weaponry and were not particularly concerned with advancing the human condition. From a military standpoint this was pragmatic, but it actually retarded scientific progress that could have been far more innovative.