Probably because I've enjoyed fantasy my entire life. I played D&D first edition as a youngster, Wizardy on the computer.....things like that. My son played Oblivion and loved it, but I never gave it a try. I didn't really pay attention enough to realize what it was. Then he got Skyrim for the X-Box soon after release and played it and played it and played it. Once again, I didn't really pay attention at first.
Finally, I gave Skyrim a try. I think I got frustrated early on when my original character became a vampire. I had no idea where to look for anything and was just lost with people attacking me on sight. I put it down and didn't mess with it again for months. Maybe even a year.
Then something happened where my son brought the game up in discussion. He knows my love of fantasy as there has been LOTR, Dragonlance and Drizt items throughout my house all of his life. I told him about my run-in with this vampire business and he gave me a suggestion to use a previous save and then he'd show me how to cure myself. I was still overwhelmed with the size of the game so he sat with me through a few sessions teaching me how to operate in the game. From there, I didn't look back. I did take a long break this year, having put it down in March and only picking it up again within the last month. I believe part of my problem at first was that I didn't appreciate the wide open game that it is and always felt like it was taking me forever to do anything or get anywhere. Now I see that as part of the fun and enjoyment of the game as opposed to a negative. I was trained to think there is a clock ticking in a game. There is a timelimit to be beaten. Obviously, not so in Skyrim.
I play it because this type of stuff suits my fancy. I play it because it can be what I want it to be, either rushing headlong into a fight or chilling at the house bending metal, hunting game or simply hanging out in a pub. I play it because there is only one idiot and that's the guy holding the controller.