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...
In the near future bitcoin can not increase 20k, but for long term I think bitcoin will be able to reach 20k. The market is currently unstable but nobody knows the stratus of the market in the future, and it could be that bitcoin adoption is increasing and can make bitcoin reach 20k. Whatever you choose, it depends on your belief.