Or the owner might just have died or might be in prison. I'm pretty sure that the reason for not moving those coins is because BTC is radioactive. It might be partly a reason, but surely not the only reason. If you really needed the money you could try several methods to launder them.

You could try, but miners aren't going to include a transaction from that address in a block, especially not to some sort of mixing service.

It takes something pretty extreme to get the consensus of enough miners to matter, but the hack of Mt. Gox was that extreme.

This is not true.

We'll probably never find out, but there are plenty of blacklisted addresses miners won't touch. Ignorance of this is revealing.

What miners are blacklisting addresses? $623m in hacked Bitfinex funds were moved today without issue.[1]

[1] https://www.coindesk.com/623m-in-bitcoin-from-2016-bitfinex-...

Transactions are broadcasted well before they are included in a block, so we'd know immediately if it happened.

I am deeply familiar with these systems. Maybe there are miners out there doing this, but it's not widespread enough to have any impact.