The movie invented the zombie genre as we know it today, was made by George Romero, which is a credential in an of itself, and Duane Jones' performance as Ben would stand out today almost as much as it did back then. These points, along with the film being poignant and entertaining as hell would ensure that generation after generation would would keep coming back. Remember, lots of films are out of copyright. Not a lot of such films made as much money or have the staying power as Night of the Living Dead.

On top of this, genre films in general, and horror specifically, if anything, have rabid fans that go out of their way to watch movies because of their genre, regardless of accessibility or buzz. Again, George Romero's involvement alone would make sure that even a passing fan of horror (or budding cinephiles) would seek it out.