FATE Paradox (Reasons for)
A ghost worker at Chronopolis reveals that FATE employed the Records of FATE to prevent citizens of El Nido from accessing mainland Zenan, lest they cause a chain of events that would result in Chronopolis's never being built in the future. The system of time used by the Chrono series naturally abhors paradoxes; why is FATE threatened by such a problem in history?
Shift Disaster Possibility
Under Bubblebobby2000 and GrayLensman's theory that the entire Sea of Eden was realigned with the world of ten thousand years in the past, and judging from the Dead Sea's creation in Home World, it can be inferred that whatever occurs in the future will have a direct impact upon the Sea of Eden, which, since it exists ten thousand years beyond the outside world, would directly reflect the state of things. The Dead Sea was created simply because Lavos destroyed Home World beyond 1020 A.D. after the dimension came into existence. FATE fears that irrevocably changing the future will cause a such a disaster, and that Chronopolis must be created under the same conditions present in Keystone T-1. This does not mean that Chronopolis's existence hinges on probability or possibility.
FATE cannot cease to exist by possibility alone; this contradicts the way time works in the Chrono series. For instance, while free will exists, time is not random. Crono and crew traveled to the same 2300 A.D. with the same people; there was no question of random possibility of new people existing or the old ones being arranged differently, as once time progressed beyond Crono's original departure, the events of the future played out and resulted in the ruined future seen in 2300 A.D. Mere possibility cannot act as a trigger for changing history; something material is needed. Since Lavos emerged in the future of Home World as soon as it was created, the Sea of Eden turned to the Dead Sea.