They're going to Clubhouse themselves by being stingy with invite codes.
Wasn't the thing that killed Google+ that it just didn't have enough engagement for it to be worth for Google to run it? I seem to remember that at the time, Google was saying that 99% of the user sessions were less than a minute, or something like that, and that's the reason they are shutting it down. If I remember that correctly, it seems it wouldn't have mattered if they had a Beta label on it or not.
That and the ill-will generated by forcibly cramming it down everyone's throats a la the youtube debacle.
Guess my age: I'm mad at Google for 1) Reader 2) Breaking + as a search operator