Every market like stocks commodities Interest rates etc see corrections upto 75 % which doesn't mean that they will not go back up higher and history proves otherwise. These corrections in fact are healthy. There can be many many factors behind these moves. Bitcoin being the first crypto with early mover advantage and with improvements like Lightning Network in the works, Bitcoin will keep growing and will see new highs in the near future.
OP is totally right. With corrections like these, we are bound to return to $20,000. But we just have to be patient, though. Sooner or later, the market will bounce back to $20,000 or more. Just hodl long enough and prepare some cash to buy some bitcoins.