Because there's only so much text writers can put in quests and dialogs, and they'd rather use that place for stuff relevant to this expansion rather than content from over 10 years ago.
You probably realize what you see on screen isn't the full extent of our interactions with NPCs we would have this conversation with. But it would be kinda weird to speak to a new NPC and he casually drops "wow btw the moon was super big for a time, crazy huh?".