The reality is that they would not have been able to hold for so long even if they bought 10 years ago. Very few have the patience to wait till 100x or more. Most of the investors will be sold at the idea of 2x or 3x itself. Some of the people that were able to hold for so long were those who had invested and then completely forgot about it. There is one more category of people who had complete trust on BTC and thus they stick with it for years.
I think this is the same case with every investment where its price skyrocketed in the market 5-10 years ago.
I started investing in BTC back in 2017 where its price was relatively equal to roughly ~$4,000. Unfortunately, if I had just HODL my BTCs, I would have earned roughly around ~$40,000 in BTC which would have helped my family in relieving the expenses incurred.
Though this may be the case, this fully taught me on how to HODL my BTCs for long-term gains. Given the inflationary nature of BTC, its price would inevitably skyrocket the more it reaches to the points where every BTC would be mined out.
The most BTC I had ever acquired was roughly a little over 0.50 BTC, not a huge amount, but decent nonetheless. Do I regret spending them back in 2013? I do, however, OP's point is valid, we'd probably have sold when the price doubled or tripled. I remember buying at approximately $300-400, chances are, that I'd have sold them by the time it reached $600-800.
No one could have predicted that in 2021, Bitcoin would be worth a fortune, there's no point in regretting, nor thinking what we could have done differently. There's no way someone could have held for so much time, let's not forget 2017's all-time high too, which was the point I said to myself that it can't go any further, and decided to sell a good portion of my BTC.