Concerning Nick's feeling responsible for getting people to attend Gatsby's funeral in The Great Gatsby, Nick likes and admires Gatsby throughout the novel. He at one point says that Gatsby is worth more than all of the other characters in his narrative put together. He simply feels that Gatsby deserves a strong showing at the funeral.
Nick also believes he sees something in Gatsby that others don't. Psychologically, particularly if we recognize that Nick is an unreliable narrator, this gives Nick a feeling of superiority. He alone recognizes Gatsby's worth. He comes off as a better person because he gives Gatsby the worth and homage Gatsby deserves. He believes he sees the truth about Gatsby.
Also, the novel is in part a satire. Nick's emphasis on the contrast between the hordes of people that used to come to Gatsby's party with the hordes that stay away from the funeral points to the Jazz Age self-centeredness, shallowness, and frivolousness. It also points to the hypocrisy of Daisy and Wolfsheim.
Nick's feeling responsible for getting people to attend Gatsby's funeral also, by the way, reveals Nick's continued naivete. Not that he tries to get people to attend, but that he is surprised when they don't.