4) People die. Not even talking about CIA black team stuff. Maybe bad luck he walked out in front of a bus and since nobody from his "real life" knew the connection to Bitcoin and nobody from Bitcoin world knew his real identity we will just see that as a founder who simply never communicates ... ever.
But he made a clear exit before disappearing. So if he died shortly after its coincidental.
ONLY 30%. Those first year coins are concentrated into only several dozen people's hands. Some never thought it was going anywhere and deleted the wallet. But that can't account for SO many unmoved coins.
2.6 mil first year coins. At least 600k mined by Satoshi, mostly in the middle 6 months when difficulty was anemic and a handful of computers would score half the blocks.
2 mil mined by other early adopters, 500k deleted (25%) because they thought they wouldn't go anywhere. That leaves maybe 1.5 mil that hung on. Assume they as a group sold at least half in the various run -ups (750k). That gets you to about 30%. Not much room there for Satoshi to do much selling.
By early 2010 the difficulty started to shoot up, so his computers probably were only scoring a handful of blocks/day at most, and by middle to end of 2010, looks like only maybe one or two a week. So most of his coins were made in the first year.