I won't opine on the correct value of the stock market at the moment, but the drop in demand due to measures needed to preserve life
cause a financial issue. Many/most consumer-facing businesses can't withstand a drop in demand to near zero for a period of at least several months. So those businesses, absent some sort of national bailout, will go bankrupt. Or at the very least, they will go dormant. Either way there will be layoffs, and of course the laid off employees will reduce their spending further. Even once the virus is under control, it will take time to reverse this damage.
Yes, of course, the market won't go to zero. But some firms will go under, and we don't know how severe the economic impact will be. Just because the crisis began with a natural disaster rather than a financial one doesn't mean there can't be serious financial impact.