Maybe it doesn't make sense for some people, but put yourself in the position of someone who mined BTC practically at the very beginning with his personal computer and actually spent only a little electricity and his time. Maybe he needs that BTC at this very moment, and maybe it's just that he wants to move it to a more secure storage.

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Be that as it may, you shouldn't worry too much about the fact that transactions are taking place with coins from the earliest blocks, because we know that there are people who have control over these private keys even today. The fear that Satoshi will suddenly dump his coins is completely unjustified in my opinion, because if he created BTC only for his own profit, he would have profited long time ago.