The guy owns a million of these damned coins, and each new person he gets to invest pumps the value even higher. Maybe hes worried about public scorn when the bubble pops and investors lose money? The guy is essentially getting the best of both worlds: filthy rich and doesnt need to answer to anybody.
I cant imagine that Satoshi ever dreamed this would go so well, but its food for thought. Id like to know his rationale for holding onto so many of the coins. Is his goal just to bring the price up as much as possible? If so, why?
Satoshi can't spend his coins without risking his anonymity.
Most of his coins are in blocks of 50 btc as the unspent block rewards from all those blocks he mined early on. He could cash out one of his later chunks of bitcoins without anybody knowing it was him. One block reward would be something like 32 thousand dollars right now, that is enough to live on for a year.
Additionally, he could just sell the coins OTC for cash and remain anonymous.