The reason for the difference is that the 2nd biggest holder is likely poloniex, and they don't stake their coins at all.
I never understood why they wouldn't stake and take a 10% cut of coins earned or something.
They make more money and they help decentralize the coin that they are risking their asses on by accepting deposits...
Somehow they're already making enough money that the extra 10% here just fell below their radar? I dunno. It is surprising that they wouldn't stake on reasonably valuable POS altcoins that they support.
Looking at their volume and trading fees, I could understand how 10% of staked clams is rather insignificant and not worth the effort. Plus, if they were to sell those earnings on their own exchange, it surely would cause some shitstorm and (valid) accusations of driving the price down.
Or maybe they just trying to avoid gaining >50%?
Do they stake any other PoS coins?