That's what happens with an asset that has given such a return as Bitcoin. There were many people who knew about Bitcoin when it was worth very little, who had the opportunity to buy and didn't, or bought and for some reason or another sold, and now think about how much of a multi-millionaire they would have been if they hadn't done so.
I think even those who believed in the technology themselves didn't imagine that the price of 1 BTC would reach more than $60,000 someday, or else they wouldn't have sold. They would have accumulated more instead. Even Hal himself who thought that Bitcoin could reach as high as $10 million converted a lot of BTC during his lifetime. Perhaps they considered the possibility of Bitcoin becoming very expensive as remote, so much so that they didn't think twice of selling when Bitcoin was as cheap as a hundred dollars.
I think no one knows way back then that bitcoin market value will going to soar high like the current price. Every one has their own kind of story of regret that they did not able to catch up bitcoin at the time that it was affordable by many but in the case of OP I think if I am in his place way back that time I will be having a second thought also even let's say I am a professional trader of stocks and knowledgeable enough about trading, aside from the huge amount of investment which a bit sound shady if we will be in that place while we listen to him, crypto platform was just new that time.