Because that's for you to discover, they lived all those events already, there not going tell every guardian what they did, you hear through lore, whispers, legends, weapons, and the deeper stuff is hidden and you have to go find it. Just like if your in a library you need to search for the information. Again the game was meant for Hardcore Lore players. I respect your view on it, but it's how the OG writters wanted the game.