I personally love that my character has a blank slate past, with nothing more than an origin to select in character creation. This leaves me open to come up with whatever backstory I want, enhancing my role-playing experience. I don't care how good The Witcher is, I'm not interested because I don't want to be forced to play a pre-made character like Geralt. Let me make my own character and decide my own story.
Oddly enough you totally nailed why I don't play it either. And never was tempted by Mass Effect or any similar "play THIS character" type of game.
Lots of the fun is creating/exploring my new character (or depending, my reincarnation of an older one).