How can we convince business leaders to encourage employees to work from home, or community leaders to cancel events? A challenge is that the official sources I've seen are not recommending cancelling events yet.
It seems as though event cancellation is now the general norm, so hopefully the situation you outlined is quickly changing.
I don't know what the circumstances were behind any given cancellation, but it might be valuable to look for stories about contentious events (e.g. St. Patrick's Day parades in large East Coast cities) and see if you can pinpoint the reasons that they were shut down.
Similarly, you could look at statements from prominent companies that now encourage employees to work from home (e.g. Alphabet) and see how they explain themselves. (The prestige of those companies may also be a good selling point for other business leaders.)