Take a look at these two graphs. The first gives the number of new COVID-19 cases from John Hopkins University. It is a scary graph.
https://coronavirus.jhu.edu/data/new-cases
The second graph is the number of COVID deaths from IHME. Not nearly as bad.
https://covid19.healthdata.org/united-states-of-america
CDC reported death numbers are similar. In fact, the number of deaths in recent weeks is no different from normal according to the CDC.
https://www.cdc.gov/nchs/nvss/vsrr/covid19/excess_deaths.htm
One reason for rising cases is that we are doing more testing. Thus, we are catching more cases. People who are hospitalized with critical illness are more likely to be tested and thus as we expand the number of tests, we are now catching more of the less severe cases with the additional testing.
However, testing does not explain everything. We see that as cases are rising, so is the number of hospitalizations. Thus, this is not just a testing story. Real–not just detected–cases are rising.
https://twitter.com/Trinhnomics/status/1279948543684313088/photo/2
Most likely, the existence of more effective treatments (e.g., remdesivir and dexamethasone) and physicians gaining experience treating the disease is responsible. Among hospitalized individuals, death rates have been falling dramatically in recent weeks.
https://www.bbc.com/news/health-53192532
There is much still to be learned about the causes of these divergent trends and much more research is needed.
Improved treatment MAY be one reason for lower hospital fatality rates from COVID-19, but another possibility (to my mind, more likely) is a difference in the demographics of patients hospitalized. Recent reports have emphasized the younger age of those now being infected and it is well known that the mortality rate of COVID-19 increases with increasing age. Also, over 40% of deaths from COVID-19 in the U.S. have been among nursing home residents, who are both older and more likely to have comorbid conditions that increase the likelihood of severe disease related to COVID-19. With continued restrictions throughout U.S. nursing homes, the number of new cases in nursing home residents is likely limited, further reducing the case-fatality rate of new infections.