They are certified hodlers, not into rush and they know when to unload. It means that there are plenty of Bitcoins when FOMOs rush into market. Theres always buyers when those 10 million are unloaded.
They might be or maybe the owner of that is already dead, which I hope not, I mean that is just a speculation. As far as I know, these HODLers like to move their huge amount of bitcoin from wallet to wallet, and they don't usually put all of it in one wallet, they cut it into pieces and manage with different wallets. that is 10 million bitcoins, almost half of the total supply.