Notch announced that it was never his goal to create something as big as Minecraft, he thanks all fans and explains he no longer wants to be responsible for huge projects that he doesn't understand and that keep coming back to him.
Notch explains that part of the reasons for his decision to leave was the backlash over clarifications in Minecraft’s EULA statement, which prevented server owners charging for various in-game services, and a fear that his career trajectory would take him to the same places that Fez developer Phil Fish ended up in.Source: Bit Tech
’I didn’t have the connection to my fans I thought I had. I've become a symbol. I don’t want to be a symbol, responsible for something huge that I don’t understand, that I don’t want to work on, that keeps coming back to me,’ said Notch on his blog. ‘I’m not an entrepreneur. I’m not a CEO. I’m a nerdy computer programmer who likes to have opinions on Twitter.’
After the deal closes, Notch wants to go back to smaller Ludum Dare prototypes and small scale projects, going as far to say that if he ever starts accidentally creating something that gets as much traction as Minecraft, he would most likely abandon it straight away.