here's a correlation, make of it what you will.

1) SARS-CoV & MERS (both coronaviruses) death rate higher, contagion lower. SARS-CoV2 (COVID-19) death rate lower, contagion higher. Relatively.

2) Statistical research into the evolution of infectious diseases (seen on TED.com) found that diseases that are more likely to kill its host, in counties that had infrastructure that thwarted the spread - evolved to be more benign, less deadly.

There are reports that think that the intermediate vector for COVID-19 was via pangolins.
Bats 7 degrees of difference, pangolins 3 degrees of difference (markers). Bats carry many viruses that don't seem to cause too many problems for them.
Early days, given there are more pressing problems in fighting the pandemic.