Looks like the whole thing was a bit of a s**t show. Fans were left waiting at the gates while F1 staff waited until the last minute to make a decision. Very inconsiderate for the fans, not to mention it put them at risk of catching something while waiting (i.e. instead of making the decision earlier and informing the fans not to come to the track).
It also seems some drivers started making their way back home before the official announcement was made, further reinforcing an announcement could have been made earlier.
https://www.racefans.net/2020/03/12/...be-allowed-in/