I don't know what it is but I just couldn't get into Witcher 3 as much as other games. I played for about a week about a solid 10-15 hours into it. I love the game, the graphics are great but everything else feels unintuitive. From a distance Witcher 3 looks amazing but the closer you get the messier it becomes. Oblivion was my life for 2 months. Fallout 3 had me hooked from day 1 and I couldn't stop until I beat the story. Skyrim took away 400+ hours of my soul. Bethesda games just know how to make me open the game. With most games after I stop chain playing I just lose interest in launching it. With Bethesda the first thing I think about when I get home from work is launching up Fallout or Elder Scrolls.
That's damned right.
What you've discovered is that The Witcher 3 is soulless. As you said, Fallout 3 just sinks its hooks into you from day one, and doesn't let go.
Fallout 4 is going to demolish The Witcher 3. Bethesda is going to school CDPR.