A writer may repeat himself in both matter and form over half a decade. The talent of a filmmaker, [however], if he does not evolve with his art, lasts no more than five or ten years.
A writer needs only a pen and paper to write. This, regardless of his work's popularity, he may continue to write however he pleases. However, as Tarkofsky notes, film is a medium enslaved to money. To make films, you need a minmum amount of resources. Money comes from viewers, tastes of viewers change. Thus, a filmmaker, even if his motifs and apirit are the same must adapt to the changing tastes of viewership order to make films.
This is why Nolan uses big cinema to house his philosophic and emotional musings. Yes, his films are full of tropes and business stereotypes. However, his ideas and questions, because of the shell of Hollywood technique he uses, are open to thousands more than any independent film he will ever make again.