There are many possible reasons but I'll just list three. (1) Pump and Dump schemes. The industry is unregulated so any money making tactic, even unethical is not illegal.

(2) Roger Ver (Bitcoin Jesus) just said "Insider Trading Is a Non-Crime". He was speaking of the recent insider trading allegations against Coinbase insiders who may have traded bitcoin cash early and leaked info. This news reduces confidence of ordinary investors.

(3) It's a young market and this is normal shakeout. Bitcoin "crashed" at least 6X in 2017. Each time was predicted as "the bubble burst". And each time it has roared back even stronger.

So it your strategy is HODL, this is part of the business cycle.