Earth's timeline

The Time Lords understood that the planet Earth had a unique timeline. During the Last Great Time War, they used the Matrix to project the post-Time War universe and thus foresaw Big Bang Two, which they knew would cause subtle changes in Earth's timeline resulting in the memory of high-profile alien incursions such as the 2009 Planetary Relocation Incident being forgotten, such that humanity at large would remain unfamiliar with the Daleks as evidenced during the later Security Drone Incident of 2021. (PROSE: Dalek Combat Training Manual)