Its probably because many have lost there keys while others don't have a place to spend and are accumulating them as an asset of investment. There will be total supply of 21 million and if this figure 10M bitcoin is true then this means many are hodling bitcoins for day to come. Though I doubt these stats.
It wont really be that precise on having that 10M coins havent moved out yet we should consider those which are lost or floating to void
but if large part of the entire number is still accessible then it wont be a surprise if there would be a crash on price i majority of those holder
would tend to secure profits on a specific time.As said this might happen before the halving event commence.
http://diojrat.com/blog/طلای-اب-شده-چیست؟/