Okay, have they ever had to close streets before, and how many people would have to attend for them to make that decision?
Yes, they close streets for a lot of thinks - farmer’s tractor protests, festivals, whatever. It’s no different than the cops in your town closing streets when the high school football game is being payed and the crowd is assembling. You don’t want cars trying to snake through hundreds of people. You divert them down the street.
In Washington, you also block streets just to keep people at these events from parking there.