Simply because the WHALES take the profits whenever there's a 5 to 10 percent growth. The bottom line is Swing trading and Day trading is real and the HODL method is just what it is...
Your logic here lacks substance - don't you think that taking profits from bitcoin trading/market movement when the price will be 20k or 40k would be much better for the whales?
I just remind everyone - current bitcoin price is still much higher than most of us predicted. Just see this prediction of Bobby Lee from 26. Feb 2017:
https://prnt.sc/jisztbHe said that Bitcoin price would reach max 11k USD in 2020 after halving - so even whales have no idea how the price will shape in the future.