Viruses evolve. When they evolve they go out into the world, and they only survive if they're successful. Say for example the coronavirus were to evolve into one that killed the host in ten minutes. The virus would probably die out because the host has died.
So, weaker coronavirus forms are more likely to spread because people are more likely to go to work, go out, do things and therefore it will spread more.
However once you've reached the point where people don't care too much, then it doesn't matter how weak or strong it is, it'll still spread and still be successful.