I'm not any epidemiologist, so if someone knows more please correct me, but I read that viruses with a high mortality rate are much easier to contain. Mainly because the virus more naturally dies out as it kills its hosts. That was one of the reasons that SARS didn't reach pandemic scale with its 10% mortality rate.

I have to wonder if Covid-19 is in the 'sweet spot' of dangerousness, as it has a mortality rate that doesn't hamper its ability to spread but still kills a lot of people.