It really depends how many people are flying in from out of town for the event, otherwise the same logic leads to shutting down all schools and stores.
https://www.businessinsider.com/four-us-coronavirus-cases-li...
The recent Houston area cases were from a group that traveled to Egypt recently; I'm sure at least one person in that group was interested in going to the rodeo, which averages about 2.5 million attending each year: