They don't release the data because if they did, then the gov fears the jail would then start mis-reporting their data or obfuscating the actual data. By doing so, they kind of give a pass to the jails in order to get them to report more accurate numbers.

But don't worry, Reuters did their own data analysis:

Because the government won’t release jail-by-jail death data, Reuters compiled its own. The news organization tracked jail deaths over the dozen years from 2008 to 2019 to create the largest such database outside of the Justice Department. Reporters filed more than 1,500 records requests to obtain information about deaths in 523 U.S. jails – every jail with an average population of 750 or more inmates, and the 10 largest jails or jail systems in nearly every state. Together, those jails hold an average of some 450,000 inmates a day, or about three out of every five nationwide.

The results were predictable:

Reuters is making the full data it gathered available to the public.

One finding: Since the last Justice Department report, for 2016, the death rate in big jails has continued to climb, leaving it up 8% in 2019, the highest point in the 12-year period of 2008-2019 examined by Reuters. In that time, the suicide rate declined as many facilities launched suicide awareness and response initiatives. But the death rate from drug and alcohol overdoses rose about 72% amid the opioid epidemic.

So alcohol and opioid OD's accounted for most of the deaths. Not mishandling by the staff or as the first story in the article highlighted, an inmate who was beat to death by the prison guards.

Which begs the question, how are drug addicts ODing while they are being incarcerated? Don't they have resources to get these people help with their withdrawal and treatment??