Just as the majority of people here have given death and lost of access to the wallet holding these coins to be the reason why those coins haven't been move for a long while, another concrete reason for me why I think there coins haven't been sold or touch for this long period of time, is maybe the owners of these coins have not got need for it yet, that is maybe they have a target amount they intend to hold Bitcoin before selling.  Just as in the case of "frank1" above who says he has been holding his coin since 2012, of which this method can also be applicable to anyone, you don't need to hold a whole full 1 Bitcoin, any fraction of it is likely okay, only if you could have the mindset to hold it for a very long time.