He may also have taken out a loan from a traditional financial institution and used them as collateral.
There is a very real possibility that they are in fact owned by someone else now, who has made the same exact calculation you have - they are a valuable asset that has exactly zero liquidity.
Are you trying to claim that someone would buy Satoshi's coins without moving them to a wallet they control?
In this scenario, the person would have 'purchased' the coins with precisely zero assurance that Satoshi wouldn't just move them to a new address at any point, as he/she/they still have the private keys.
As I said, it is impossible to verify that that isn't the case. He could have taken a loan with the whole wallet as collateral. That isn't the same as claiming that Satoshi did that, but it's not like the audibility of the blockchain spreads all the way to the real world. There's really no saying what Satoshi has done, and the anonymity means there's no way to find out.
It's like trying to sell an account by selling the password to it. The first thing you do is change it so the previous owner can not get in anymore. Before you did that you can not be sure that you are the only one with access. On Bitcoin the only way to change the password is to move the funds to a new address.
Example: I own one coin. I sell my private key to you for $5k fiat. You take my private key and sit on it thinking it’s yours. After a use a copy of the private key to transfer the coin to a new wallet I own. I’ve now stollen the coin I supposedly “sold” to you.
What am I missing?