Had this tournament been on outdoor hardcourt, grass or clay and Nadal definitely would be able to have won it, several times even. Nadal has the 2nd best record vs. top 10 players of all time, only short of Borg's record. Federer is 4th.
Indoor conditions are in a way perfect conditions for tennis. No sun, no wind etc. In November traditionally tennis is played indoors on hard surface. At least in Europe and most of North America which are the most obvious and deserving destinations given the history.
It's nobody's fault Nadal couldn't win it so far. Lately the surface is not that fast. Wanna see a fast indoor court? Check 90's Hannover WTF. And I'm sure he would prefer the current surface over grass for WTF. Grass and clay aren't really options for WTF. Or you mean indoor grass?