Officially, he left because the board shot down his plans for a new office. Like, right after the board told him no, he said "well, I quit then". Unofficially,

Officially, he left because the board shot down his plans for a new office. Like, right after the board told him no, he said "well, I quit then". Unofficially, he was burned out, and he used that as his excuse to quit. (the new office was probably why he wanted everyone to relocate to SF, so everyone could come work at this huge new office he wanted for the team)