Like I said, it's not that you can't justify it at all. It's that, for the majority of character types, those justifications break character. That feels out of place to me for a series that espouses the ability to play the character you want to play.
For this, I think we need to clarify the distinction between the player, the player character, the game, and the activities in the game world.
A player should be able to accomplish anything the game allows. Some things may be exclusive to each other, so a player that does one thing with a character may or may not be able to do that other thing with the same character. But the player always has the option to do something the game allows them to do even if it means making a different character.
For a character, this is where a proper skill system comes into play. A character that focuses heavily into magical and/or rogue skills shouldn't be able to become a master swordsman just because they want to. No matter how badly they want it, a character who's been studying magic all their life shouldn't have the martial skill to become head of a Guild of Fighters. A character that chooses to act against a guild, or doesn't follow the guild's philosophies, shouldn't then find that guild welcoming them with open arms.
So I agree that a character that's not set up to accomplish a task shouldn't be able to accomplish the task, but you (the player) should always have the option to make a character that can accomplish that task.
But like I said about why I like Daggerfall, simply by virtue of being an adventurer, you're doing something that not everyone can do (both in the real world and the game world). And being a good adventurer is even rarer than that. Without any story components, you're already given a character that's extraordinary, and it's up to you (the player or the character) to make what you want out of that. There's no predetermination of getting exactly what you want, and you can fail. And that's what makes it interesting. If you already know exactly what you're going to do, and you know you can't fail to do it, it's going to get old quickly.
I'm not saying we shouldn't have fantastical stories and plots. I'm totally with you in liking TES because it's unabashedly high fantasy. All I'm saying is that the world-ending plots, where only you're able to save the world because stories written centuries ago said you would, work against making things interesting to me. It diminishes my character because it's no longer about their skill and abilities or what they've done, but because some unknowable power pointed in their vague direction. You're right that Daggerfall was much more than a mundane power struggle, but my point was that everything that goes on has a logical basis, I (the player character) did things because I took the initiative to do it, I succeeded because I was good enough to succeed (and it is very much possible to fail), not because some god decreed that I would save the world.
It's the difference between studying hard for a test and risk failing the test, and then getting one of the (if not the) highest score in the class, versus trying however hard you want to and getting the highest grade of anyone in the school's history because your parents paid off the teacher last month.