What do you think these other things could be?
I generally assume he was moving on to battle an illness, and that he lost the battle and died.
Yup, that is pretty much the most common theory. After all, who among us can have billions in a wallet and not move a single coin for years and years? If he did not die along the way, the he certainly has the willpower of a god.
I prefer to assume that he is alive and well, obviously this presents the question of how can someone have so much money and not touch it? But there are several explanations, satoshi knows that if he moves his coins then the whole world will know about this in a matter of minutes and if he begins to cash out this will create incredible FUD as everyone will wonder why the founder of bitcoin is cashing out, and an even more important reason is that the authorities will probably want to find his real identity if tries to get to his coins and you can be sure every single intelligence agency will try to find him.