Perhaps the person (or persons) is concerned that bitcoin will become even more successful and will threaten powerful institutions like major world governments.

Perhaps the person (or persons) is concerned that bitcoin will become even more successful and will threaten powerful institutions like major world governments. I wouldn't want to be Julian Assange right now, and that is a perfectly sensible reason for the inventor of bitcoin to wish to remain anonymous. A different reason might be a fear that if a single inventor were known that bitcoin would become vulnerable to "change it this way because the founder says so" attacks, weakening the decentralized, P2P nature of the currency. (This is a less plausible reason, but still valid.)