I don't think you even need a detailed RAW explanation for why such-and-such a spell doesn't work (or why you should be able to break out of the main plot by level 3): it doesn't work because that's what the game says. My first experience of GMing was the Wildemount module Frozen Sick, and in the introduction text the players are told that there's a mysterious disease going round and none of the local clerics were able to cure it. The players all accepted it: this disease can't be cured by standard magic. If any of them had sat there going "but why doesn't Remove Curse fix it?!" all session, I wouldn't have bothered to run the game.
