The game has sold 54 million copies across all platforms. In the past 24 hours it has sold more than 8000 copies on the PC alone. And the number is increasing every day. Notch is already a millionaire and has been for a while.
Everything must have its price but even from a business standpoint I don't see why anyone should sell such a profitable venture unless they already had plans to stop adding new content to the game and were just looking to get rid of it.