Because if it does it has some interesting consequences: 1. Vault 13 has one (information from FO2). 2. It can clean water (information from FO3). This makes sending the Vault Dweller for a water chip and in turn starting FO1 at all pointless. Therefore he does not leave, is never banished, Chosen One is never sent out to save Arroyo (might not even be born) and does not blow up the Enclave. They, in turn are not defeated and not forced to move east, so the events of FO3 never take place. Or in simpler terms: If Fallout 3 is canon then Fallout 3 is not canon. Could you please point out the holes in this theory and the wrong assumptions that I have made and make it stop bothering me? Thank you.