They're shutting it down precisely because no one was depending on it. How would anyone depend on a social network without any users?
It did have users. I have no idea the exact number, and clearly it wasn't as many as Facebook, but it wasn't the ghost town people always made it out to be. Some of the Communities were actually quite active.
There are a lot of RPG communities, and a lot of roleplayers and RPG designers who don't even use Communities because G+ already is a community. Communities are a later addition, and G+ works fine without them.