Reason # 1 - I have not used fast travel once!
Personally, I would have liked to at least been able to fast travel to the major cities like I did in Oblivion. I like to know that I have a safe haven somewhere so I don't die. It's very hard in Skyrim to get where I need because certain areas are lvl 10. So I have to find my way around them and then end up in weirder and more difficult situations.
Reason # 2 - I haven't had the urge to restart my character!
I restarted my Skyrim character a few times because it just isn't what I want.
Reason # 3 - I have not taken advantage of the save system!
I have had to save before every major thing I do. Because it gets difficult if I cannot sneak.