You act as if characters in a videogame have ever had any motivation other than being the player's [censored].
Well, I play primarily RPG's, and those usually are pretty good in the story department for motivation to climb Mount Doom, if I may use the anology. Most videogames though, yes, don't offer a lot of reason why you must first travel through the Lava Level before crossing the Ice Level.
I like my heroics to have a reason, and that's why I play a lot of RPG's.
Or even a ludus.
See for me I like it when characters lose their soul. It's kind of a classic Greek approach I take. Like Hercules and his wife's unfortunate end. Most of characters are alcoholics or have anger issues or great depression or struggle with losing their religion....something. I'm a pretty happy guy so I find happiness rather boring.
I'm a svcker for a happy ending, or at least an ending that dictates "The long journey is finally over..." or some nonesense like that.
Now on occasion, I have made the Anti-Hero, who was more satisfied with simply ensuring that other people had peace rather than myself. But either way, I'm a fan of the Heroes story.
That was one thing I enjoyed playing Fallout 3, and a philosophy I will carry with me into New Vegas, and any other Moral-themed RPG, is that my challenge is to maintain my humanity in an inhumane world and do good deeds where others will succumb to greed and temptation.