Why are alien characters usually presented as superior to humans in science fiction?

Isaac Asimov once explained that his reluctance to write about aliens came from an incident early in his career when Astounding‘s editor John Campbell rejected one of his science fiction stories because the alien characters were portrayed as superior to the humans. The nature of the rejection led him to believe that Campbell may have based his bias towards humans in stories on a real-world racial bias. Unwilling to write only weak alien races, and concerned that a confrontation would jeopardize his and Campbell’s friendship, he decided he would not write about aliens at all. Nevertheless, in response to these criticisms, he wrote The Gods Themselves, which contains aliens and alien sex. The book won the Nebula Award for Best Novel in 1972, and the Hugo Award for Best Novel in 1973. Asimov said that of all his writings, he was most proud of the middle section of The Gods Themselves, the part that deals with those themes.

In the Hugo Award-winning novelette “Gold”, Asimov describes an author, clearly based on himself, who has one of his books (The Gods Themselves) adapted into a “compu-drama”, essentially photo-realistic computer animation. The director criticizes the fictionalized Asimov (“Gregory Laborian”) for having an extremely nonvisual style, making it difficult to adapt his work, and the author explains that he relies on ideas and dialogue rather than description to get his points across.