Folks like you and I understand this. But what the general market world is going to see is doom and gloom when the number of "infected people " in the USA jumps from 100K to 4, 10 or even 20 million, because of expanded testing. The markets will see that as the end times, and crash even further on that. Algo programming or whatever.
It is not about mortality rates or anything like that. It is the preliminary number of cases, which will be extrapolated out for future economic data.
And they may be correct. 20 million people finding out they have a new flu they have not heard of and staying home for months is going to hurt us.