[michaelt]

Basically, some simulations show [1] if lots of people from an otherwise-socially-distancing population all go to one central location, that increases the R0 (i.e. spread) of the virus.

This is a problem for anything that draws together lots of people from a large area into the same place - trade shows, sports events, music festivals, cinemas, conventions, busses and trains, food stores, beaches, universities and schools.

We almost certainly haven't hit on the most optimal solution - in my country we closed schools, yet keeping crowded metro trains running? - but it wouldn't have been wise to wait for more data to come in before taking any action.

[1] https://youtu.be/gxAaO2rsdIs?t=1010