Italy went into lockdown on Mar 9.

By the end of March 32 of 50 states were mandating social distancing.

These papers are all arriving later, a fact which is everything and what's more, it's a fact which we expect and want to happen; it's called "further study" and its what science does:

https://saidit.net/s/Coronavirus/comments/3wo8/stanford_study_finds_covid19_infection_rate/ 17 Apr, 2020 22:36

https://saidit.net/s/Coronavirus/comments/3vz3/danish_blood_tests_shed_new_light_on_the/ 8. APR 2020

With the exception of this one:

https://saidit.net/s/science/comments/3i9b/nature_medicine_covid19_in_wuhan_was_14/ 19 March 2020

But in this very paper there comes this sage observation, which is the same one I am making here:

For a completely novel pathogen, especially one with a high (say, >2) basic reproductive number (the expected number of secondary cases generated by a primary case in a completely susceptible population) relative to other recently emergent and seasonal directly transmissible respiratory pathogens4, assuming homogeneous mixing and mass action dynamics, the majority of the population will be infected eventually unless drastic public health interventions are applied over prolonged periods and/or vaccines become available sufficiently quickly.

Even under more realistic assumptions about mixing informed by observed clustering of infections within households and the increasingly apparent role of superspreading events (for example, the Diamond Princess cruise ship, Chinese prisons and the church in Daegu, South Korea)5,6, at least one-quarter to one-half of the population will very likely become infected, absent drastic control measures or a vaccine. Therefore, the number of severe outcomes or deaths in the population is most strongly dependent on how ill an infected person is likely to become, and this question should be the focus of attention.

We know that the death rate may be lower than the CONFIRMED data we have at hand, you're not telling epidemiologists anything they don't know, but how much lower? We needed more information to determine that. This paper is one tiny bit of information derived from one single data point, as they explain::

Briefly, because the healthcare structure has been overwhelmed in Wuhan and milder cases were unlikely to have been tested, we used the prevalence of infection in travelers (both on commercial flights before 19 January and on charter flights from 29 January to 4 February) to estimate the true prevalence of infection in Wuhan; we also used the Wuhan case numbers from only the first 425 cases to estimate the growth rate of the epidemic

Even the authors themselves don't recommend backing off social distancing. They did one study using a single source of data. It's interesting and perhaps suggestive but not by any measure definitive enough to guide public policy.

But you're suggesting it should have driven public policy. Because that's what we're talking about here- public policy.

Public policy was and should be as conservative as is bearable until enough data is accumulated to warrant the risk of backing off. This is what this paper itself says, as I pointed out.