It's all about the enemies you are fighting. They have you fighting enemies with high yield XP rewards, but they nerf the enemies so they aren't so tough that they kill you.
So, for example, in the Nautiloid, you should fight manes and dretches, not imps. Dretches and manes are level 1 fiends. Imps are supposed to be tougher and give you more XP when you kill them.
It's that way with everything in EA. You get lots of XP for everything so you don't really enjoy each level. You rush through them so you hardly experience them or the monsters you should fight at those levels.
Well. Have you checked if they yield correct amount of XP according to RAW? I mean, I guess they have chosen the monsters because of name recognition (in the sense of recognizing the monster by name, not by the stats or abilities that monster should have) to give players not overly familiar with Dnd the feeling that they're in a DnD setting(IE, I know what an imp should look like but have never heard about manes and dretches before), and then nerfed them to fit the difficulty level. So they could have easily nerfed the XP amount given for slaying them as well.
