This disease appears to be asymptomatic/mild in the bat species it came from. Probably because bats immune systems evolved (over a long time and a lot of dead bats) to fight the disease without all the collateral damage.

This disease is novel to the human population. But we have an extreme amount of immune diversity and diversity of immune response at the population level, and concordantly some people will be able to fight off the virus without all the collateral inflammation, and others wouldn't. In a "natural" state, over time natural selection would select people who respond better, and the virus itself would probably evolve to be weaker, and eventually it would by asymptomati/mild in the vast majority of humans too.