Because we can’t trust them to tell the truth about the number of infected, but we CAN trust them to tell the truth about hospitalizations and mortality.
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What the article says is that many sick people are not being tested due to shortages. So these sick people may or may not have 2019-nCoV.
If (big if) sick persons who do have 2019-nCoV are not in need of hospitilization, and for whatever reason are either not being tested or are avoiding being tested, and big if (yikes that’s two now) they are recoving at home then the overall mortaility rate is lower than reported.
Now, the article does mention people dying of “lung sickness” who have not been diagnosed, how many total and hiw many are attributable to 2019-nCoV is unstated.
here's a short refresher course from 1989 for the above people.