"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?"
there are many reasons why they don't sell their bitcoins, the most common reason is that they lose their phase . they think btc is worthless so they forget it and they realize when btc is as valuable as it is now and they forget where to save their seeds
one thing is impossible if BTC owners never sell their BTC especially since they have already made a 1000x profit from when BTC was first introduced.