Friendly reminder: more infectious correlates to less deadly per capita unless the virus is specifically engineered by humans to be more deadly.

Natural selection pressures viruses to keep their host alive (both to spread for longer and to reinfect later) and to spread more easily.

The dangerous viruses are the ones that can live in other animals without harming them, because then there's no selection pressure to be less dangerous to humans; we're incidental. The Black Death was spread by fleas who were hardly affected by it.