Market sentiment primarily, overly pessimistic perception of the current moment which leads to fear in the market which causes investor to react emotionally eg. cut loss / panic sell..

When there are more sellers compared to buyers in the market, it will cause downward pressure in the share price. Even though, it might not affect the company fundamentally.

Investors hate uncertainty. When covid-19 broke out in Wuhan, China around Nov 2019 it was still within. Then it started to spread to USA and globally around the world.. this triggered fear and uncertainty, especially during the 1st lockdown... this fear & uncertainty in the pandemic triggered the stock market as well as it is forward looking ..