Well, as players we don't know that, do we? The Speaker explaining that to our Guardian is him also explaining it to us, the players. As far as the enemies goes, we've only just started to really explore our lost worlds again. After the disaster that was the first attempt to retake the Moon, we became reluctant to go beyond Earth to any great extent. Mars was also deemed too dangerous for many Guardians to explore (too many died at the hands of the Cabal). Since we are a new Guardian and probably had little to no prior knowledge of life beyond Earth, being just a normal citizen of the City, or someone living out in Earth's wilderness, we'd need some things explaining to us. For example, Ghost explaining some of the Cabal background to us to give us some idea of what they're about. The inhabitants of the City obviously know that the Traveller exists and they know Guardians exist, but they may not know [b]how[/b] we exist: i.e. that we're resurrected.Some of the Grimoire cards point towards internal political strife in the City (rigging of Crucible matches, for example). The fact that we were dead may be a closely guarded secret. Censorship to keep the masses happy and all that So, when a new Guardian is (re)born, a little info about the Traveller and our enemies is provided. The only race the regular citizens of the City would have any firsthand knowledge of is the Fallen because of the Battle of Twilight Gap. I also remember a card stating the Cabal were at the battle but to what extent isn't mentioned. Obviously, some of this is conjecture and speculation on my part. Still don't think playing as an Awoken breaks the lore, though.