First, because it is considered the Coens masterpiece by many and the Coens are signature filmmakers of such high importance in modern film art. Second, because it is a very unique film in its approach which makes it worthy of such a list that tries to show the best of movies in all their diversity. Third, it is hard to find fault its execution, all its elements work so well for this approach, including the very important screenplay (the coens write great screenplays since Raising Arizona, and this more reserved one is just genius), but also the acting, the characters, the cinematography, the music, the story, the scenes themselves and their sequence, its comedy, its impact, and I could go on if I tried. Fourth, in its many different elements, it is a very influential film for filmmakers, which again makes it very worthy for such lists. I guess I could think of more reasons, but I’ll leave it at that.