The Holloman Pact made the alien technology transfer contingent on launching an alien-human hybrid program. You see, the Zeta Reticulans mandate their technology to be stewarded by hybrids (similar to how China requires a 50% Chinese joint venture to gain access to their markets). The two species' geneticists started working together, and in 1971 the first viable hybrid was born: Elon Musk. Then we had to wait for the hybrid to mature, before it could be given stewardship of this sensitive technology. Meanwhile a generations-long cultural manipulation program was also underway, to prepare humanity for disclosure.