Well I've seen it discussed many times, but since you ask...

Have you never thought of the possibility that Satoshi Nakamoto doesn't exist? That maybe BTC was given to us not by a single person or even a small group of people, but by a large behind the scenes organization that sees this as a step in a master plan to achieve a bigger goal of theirs in the future. Not saying I am a firm believer into such conspiracy theories, but just that you shouldn't accept the existence of a person called Satoshi Nakamoto, who is also the creator of BTC for a 100% guaranteed fact.

Also even if he is real and all, he just might not feel like bothering with all this. Vitalik is constantly in the spotlights and people have certain expectations set for him. Not everyone wants this in their lives. Personally I'd be hesitant to reveal myself at this point if I were Satoshi Nakamoto. He's probably doing well for himself anyway, so I doubt he needs the publicity.