Satoshi created a system and keeps calling it a peer to peer digital cash if you have ever read the paper. now do you think someone with the vision of creating a currency is going to "sell" the coins.
He might die, and his heirs might care more about having a couple of billion dollars than they care about Bitcoin.
Imagine if some relative you didn't know you had, died and left you all his stuff, and going through it you found pages of printed out private keys, 50 BTC in each address. Or if you found the printed sheets in a thrift store from when they cleared out his house. I wonder how many people reading this would be able to resist temptation.