"Why haven't the earliest participants sold their Bitcoin, and some haven't even touched the coins in their addresses, considering the high price of Bitcoin?"
The owner may have forgotten about their Bitcoin investments or lost the private key that holds many Bitcoins. Some are diamond hands that still hold Bitcoin until a specific price point.
To the early participants of Bitcoin who held on to their investment even when the price was high, good luck. I hope they can sell it for their desired price and safely secure their profits.