Because it's fun

Now Notch isn't just any man. He may have created what could be called 'The Best Game Ever', but that's just the beginning. He is the Head Developer of Mojang and also created Scrolls. Notch didn't do it for the money. He actually didn't know it'd be such a success. He did it because he has passion and love for his work. One idea comes into his mind and the next thing you know, everyone's having fun. Now you might ask, what kind of man begins programming at the age seven, then a year later makes his own video game? Well, the answer is Markus Persson. Now, he thinks his success is a once-in-a-lifetime event, but I disagree.
~Jens Bergensten (Jeb)