The Answer is very simple. The $20K region is now considered a major resistance region and breaking through it will be a major milestone in Bitcoins Price history. If you expected Bitcoin to continuously rise all the way from $10K and just breakthrough the $20K price minus any corrections, then you were totally wrong. That's not how the market works.

There will always be retractions until the buying power is strong enough to push past the resistance region.
IMO, I never even expected Bitcoin to get so close to $20k this year. I think things will be greater next year.