Identifying the Issue
The Problem with Immersion
A lot of mods ask why you can run from Whiterun to Windhelm without getting tired. I agree. It's not very realistic, that you can run indefinitely, without getting penalized. But it's also quite unrealistic, that you can't run that distance at all.
So the problem is that the model provided by Bethesda simply isn't detailed enough. It goes well for short term exercise, but it doesn't consider the effects of a prolonged exercise. This is of course understandable, since they would otherwise complicate the game. But for players, who are already well-traveled in Skyrim, further complexity may add to the feel and immersion of the game.
The Problem with the Game
Skyrim is a very rich, and attractive world. There are loads of features, to make the player feel more like a part of the world. This was one of their key points, when promoting the game. And it's true. You do have the ability to do inefficient and meaningless things. And there is a lot of content surrounding these inefficient and meaningless things. As a player, I started exploring all these things. Talking to non-important NPC's, and exploring their dialogue trees just felt like a task, nonetheless. This is because it feels more like getting content out of the game, rather than what it was intended to: A break from the dragon slaying, civil warring, werewolf and vampire infested, daedra and aedra worshipping adventure that is Skyrim. An ability to just take of your helmet, and have a normal conversation with an NPC.