The top 21 has 31k btc and the last movement was in 2010
And others never sent anything. Top 54 to 69 has 12k btc each and never saw movements.
We never know, but it's also possible that the owner is no longer alive. Or, just like you said, the owner might sit around and wait for years until 1 Bitcoin equal to whatever price they think it's good enough to sell.
for instance i have coins that i received in 2014 and have not moved them ever since (5 years) that doesn't make them lost, i still own the private keys. but in the eyes of many who just look at the blockchain it is categorized under "lost coins"!
I also believe that 'lost coins' categories should only apply to coins whose private key is lost (regardless of what the reason is). We should use 'cold coins' or something similar to refer an address or coins that stuck in an address for a long time. Technically, we don't know which address no longer has accessible private key anyway.