Three years in politics is a long time if you are not a career politician and Prof. Wieman has likely accomplished all he can at a high level and may simply want to get back to direct involvement. The OSTP communications director told Nature he was leaving for 'personal reasons'.
Wieman bleeds science education. The first time I met him in person was after he had already written here and I recognized him at an AAAS conference, reading posters from high school students in physics. Did any of the young people there know who he was? I doubt it - which made what he was doing all that much cooler. I'm intrigued to see what he tackles next.
Well served, sir.