“It has been a very difficult decision not to accept Michael [Wilson] and Barbara [Broccoli]’s very generous offer to direct the next Bond movie. Directing 'Skyfall' was one of the best experiences of my professional life, but I have theatre and other commitments, including productions of 'Charlie And The Chocolate Factory' and 'King Lear,' that need my complete focus over the next year and beyond."
"Skyfall" brought in over a billion dollars at the box office and won two Oscars (Sound Editing, Original Song), putting the Bond franchise in a healthy position to attract another top tier director while Mendes is focused on the theater. The director tells Empire that he hopes to have the opportunity to collaborate in the Bond universe again, a la "Casino Royale" and "GoldenEye" director Martin Campbell.
Here's Immersed in Movies talking with Mendes.