Because its literally how market cycles work. We were in euphoria, now were plummeting back toward despair because there were no fundamentals causing us to pump as hard as we did, especially from $5-$20k.
Did bitcoins core tech suddenly become 4x as good? Did 4x as many people suddenly gain interest in the markets with a full understanding of how the core technologies work?
No. People were looking to get rich quick, and now the market is correcting back to an appropriate price.