When such research (speculation) first appeared, I think it was about the fact that one of the companies dealing with blockchain analysis concluded that all BTC that did not move for x years (I think it was 4 years) were actually lost. Then speculation began about some 4 million BTC that were "lost", of which of course around 1 million BTC are attributed to Satoshi.

When this is repeated for years, then people start to believe in it, regardless of the fact that it is practically impossible to find data that would be even approximately correct.