The unfortunate truth is, IME, there are far, far, far more players out there and DM's who think this way than think that backstory or motivation is important. I've had so many Man Without a Name characters presented to me for play. Far, far more than ones with actual thought and backstory.
And, honestly, I think it's because those players are trained from early play by DM's who insist that PC's are blank slates.
Case and point:
It's been one of the main reasons why I've pretty much given up on detailing settings over the years. Players don't give a toss and so many are just happy that the DM rolls up the plot wagon and spoon feeds the adventure du jure every session. I really wonder if I shouldn't just go through alphabetically in the Monster Manual, session after session.
After all, if the players are going to provide so little input into the game, why should I bother?