I've done this a couple of times. Yes, on occasions there was a lot of waiting/walking. But it's not a training event, more of a cultural one. Spoke to dozens of cyclists, not just from New York and the USA, but from all over the world. I even had a few pleasant conversations with New York's finest ...
Yes, people do stop in the middle of the road to take pictures, block off the whole of the road when walking up hills, etc. However, for many, cycling 40+miles is a lifetime achievement and for the couch potatoes and SUV tank drivers, a reminder of the healthy and sustainable activity of cycling as a pastime and a means of transport around the modern megalopolis.
One of my abiding memories is bowling down the Brooklyn Parkway following a whole family of cyclists, dad pulling an infant trailer and mum shepherding a couple of kiddies on their own little bikes in the midst of thousands of other enthusiastic riders. And they weren't hanging around. Where else can you see that other than in other mass cycling events?