It didn't?

Coronavirus isn't so different from other viruses as some people think. It's just like some of the many we already knew, but mutated in such a way it became easily transmissible and quite deadly. Models of how the virus spreads were already quite accurate, and were quite good at predicting how the virus would infect the world.

I think we learned the most about how countermeasures affect the spread of viruses on an international, national, regional and local level. Much was unclear about the actual effect of lockdowns, limiting group sizes, et cetera. Of course models existed, but they were never tested at such a massive scale.