"it has not achieved broad consumer or developer adoption"
I bet G+ has more active users than your average indie developer could ever dream about. But Google is not that kind of company. It's all or nothing. World domination or shut it down and try again (or buy a company that succeeded).
I'm not sure that article is saying there were 500k users. It reads more like there 500k users had granted access to an app that had these permissions. It seems hard to imagine that a bug like this would be affected by whether a user is currently active or not.
I bet G+ has more active users than your average indie developer could ever dream about. But Google is not that kind of company. It's all or nothing. World domination or shut it down and try again (or buy a company that succeeded).