Early in the cover-up on the alien presence were a few well orchestrated hoaxes, the Ummo case among them. As with most hoaxes, publicity and the resultant personal attention were the prime motivators, but when a hoax is elaborate and long lasting, other motivators are usually present. There are few opportunities for instant fame in human society - winning the lottery, making a breakthrough scientific discovery, rescuing children from a burning building, etc. The average human, even those with status by virtue of their position among the wealthy or due to being professionally accomplished, live quiet lives. Outside of the family, the circle of friends, and the immediate coworkers, no one is aware of them. For those individuals with a secret longing to be the center of attention, participation in a hoax can be it's own reward. Thus, when those who planned the Ummo hoax were looking for cooperatives, they did not have to look far!
When professional individuals participate in a hoax, for personal reasons, they do so because they are given a rationale, an excuse for the hoax, that allows them to explain what they are doing in a face-saving manner. It’s for the public safety, to help the government learn of scientists who might be contactees and thus traitors to the human race, or perhaps so the government can learn of real technology gifts given to real contactees, and thus share these gifts with the rest of mankind. Of course, the motive on the part of establishment perpetrators is greed and the desire to be in control, to retain their power positions, but this is not the way the rationale for the hoax is put forth.
Thus, the Ummo case was a grand scheme to poll the scientific community and locate those scientists who seem to be genuine contactees. What resulted, to the great disappointment of the perpetrators, was contact with yet more individuals desiring to be the center of attention, not genuine contactees receiving technology from aliens.