In "To Build a Fire," why didn't the lack of sunlight bother the main character?
The answer to this question can be found in the first paragraph of this story, where the man and the setting he is in is introduced to the reader. It is clear that the setting is described in a way that highlights its hostile nature: there is after all a "grey pall" that seems to foreshadow the tragedy that follows and it is very bleak, in particular through the lack of sunlight that there is. However, in contrast to the setting, the main character seems to be very cheerful, as the following quote establishes:
He was used to the lack of sun. It had been days since he had seen the sun, and he knew that a few more days must pass before that cheerful orb, due south, would just peep above the sky-line and dip immediately from view.
The protagonist therefore is not bothered by the lack of sunlight because he is used to it by now. Because he is so far north, it has been a while since he has seen the sun and he knows from experience that it will be a little longer until the sun will begin to show itself again, though very gradually.