[source: "primus deamon" vol14; chapter 17 pp723-725.]
The Greys, aware of the power Hobbs controlled, realized that war with Hobbs and his Daemon followers would be undesirable, likely to be violent, destructive and long drawn, made a decision to hand control of the hybrids to Hobbs.
A few months later Hobbs slaughtered the Alien hybrids himself. Realizing the potential power and threat this halfblood species might prove to be, to his own aspirations of leadership.
Declaring "unus daemon dignus interficio daemon" - "only Daemon are worthy enough to kill Daemon."