There is no direct connection between Robert De Niro and the movie 'Pulp Fiction'. 'Pulp Fiction' is a Quentin Tarantino classic known for its unique narrative and characters like Samuel L. Jackson's Jules Winnfield and John Travolta's Vincent Vega. De Niro has his own body of work in movies like 'Taxi Driver' and 'Goodfellas' which are in a different cinematic vein compared to 'Pulp Fiction'.
Well, the filmmakers had their own vision for the cast. They chose actors like Uma Thurman, Bruce Willis etc. who fit the style of the movie, and De Niro just wasn't part of that plan.
One example is 'Eternals' where he played a role. In this movie, the science - fiction elements are quite prominent, with the story revolving around a group of immortals.