What is prohibiting a national shutdown to stop coronavirus?

Food, supplies: A national shutdown would have to continue until such a time as a vaccine or cure was found. Because people need to be able to eat, obtain supplies and earn a living, it is not an option to completely close down the country. The death rate in NY for Covid is 0.5% (1 in 200). Around the country it is less. If the death rate was much much higher then drastic action would need to be taken.

COVID 19: There has been a shutdown of a substantial part of the US. For many states, only essential businesses were authorized to remain open.