Because there is always the possibility, that they can move these coins. They could have mined or moved them to a ''burn address.''
What can I say? They may just died and had the intention to burn them or spend them. I have also many questions to make, but since they're long gone, it'll only bring conspiracy theories to the table which never helped none.
What matters is that I find it highly unlikely and thus, won't spend my valuable time searching for Satoshi's supposedly purposely chosen keys to earn money. I consider more likely to become richer by digging the ground arbitrarily, searching for oil, diamonds and gold.
Why would it be unfair to give people ''the chance to reward themselves in an other way than mining'' if we have thereafter a better distribution?
How would that be a better distribution? Few folks who saw themselves as the kings of the treasure hunt become billionaires. Their keys will be demanded from Faketoshis like Wright, who'll then pretend to be Satoshi with evidence. How does that sound to you?