Hmmm, didn't notice any actual road closures* on the last ATB, nor was there any apparent traffic control of anyone except the riders. (and at that, the vollies mostly just pointed the riders down the appropriate road sometimes where there was a turn.)
*note: there may have been some at the start, but I didn't see that since BV discriminates against recumbents and forces us to start elsewhere unless we want to start at the very back.
You must not have ridden over the West Gate Bridge, or started at the official start line - both involving road closures.*
And as for traffic control, I have been on ATB rides where police have controlled motor vehicle traffic at major intersections. And whilst you may downplay the role of vollies "just pointing" - good luck finding your way without them!
* Closure - may only include closing off a lane or two, not necessarily an entire road. This all involves planning and effort, which should only be utilised by fully paid up riders.