Because some people wrongly assume that any coins which has not moved in 5 or 10 years is "lost" and therefore removed from the supply, and therefore any coins which have been dormant for this long and then "wake up" again are effectively inflating the current supply. This is obviously nonsense, as has been proved many many times in the past. The only coins which can be removed from the supply are those which are provably lost or burnt, and those coins number a few thousand at most.
The owners that have lost the keys are actually out of circulation at this time but anytime they remember the password the coins can be back into circulation and increase the supply so there is difference in these terms.As per report there are over 4 million coins lost but actually they have not the password and keys with them.
The actual coins lost are the one's which are send to OP_Return command as they can't be retrieved at all and are out of circulation.Those who are dormant address can wake up again anytime and move huge amount of bitcoin with them in transactions like you have seen.So this is reality we need to understand.