There is no definite reason, unless they are fomo and take positions rather than too late. there are still many investors who hope and predict that bitcoin will still fall, and then rise higher. it's just that, a small proportion of investors have taken positions at current prices. which is the middle price. because they still believe that bitcoin will reach a price above $ 20k.
There are still lots of people who believes that the bullish is just starting to be more stronger, and the value will rise up more. With that sentiments buying and holding while the value still in the process of retracing are what most traders are waiting, the opportunities to
get some from those holders who are now selling and enjoying their profits.
If you are into long term investment as you are doing your deeper assessment, buying and holding might be possible to consider since
the market are really forming a strong barriers and it can possibly to explode any moment in time.