[riffraff]

> cause more severe illness

on the contrary, more sever illness makes it less likely to spread, no?

You are always spreading germs around, if you have high fever or start coughing blood you'll get isolated but if you just have a runny nose you will keep living normally and the virus will happily keep infecting other people when you shake hands.

[confeit]

During quarantines people are not shaking hands. I am not saying quarantines necessarily select for a higher death rate (a dead host can not spread), but for a more severe disease (the main drivers of a spread are when people ultimately develop severe symptoms).

Community viruses mutate to see a lower mortality, severity, and infectiousness, since there is no selective pressure to have an r0 much higher than 1. For a community virus there is also no selective pressure to mutate to a vastly different strain, so the antibodies for other strains don't help, whereas if the virus is confined inside a city like Wuhan, the only way to reinfect is to mutate to a vastly different strain.