That was the problem. Orkut was successful, but that doesn't stop Google from shutting down services. Trusting a Google service to be around long-term is folly unless it's Maps or Gmail.
Google was not the giant then that it is now.
Making a social network like Google+ be invite-only when everybody was already on Facebook was an absolutely bone-headed move and I think was THE driving factor for its failure.
There were so many memes about people finally getting an invite to Google+ and then discovering nobody was there. Without your friends on it, you're not going to make it part of your daily routine, and eventually just forget about it entirely. By the time it wasn't invite-only anymore, the hype was gone and Google+ had already been considered to be a joke.
It quickly became a cesspool of racism, child porn, and other illegal activity, mostly by Brazilians, who bullied everyone else off the platform
Google tries many new products (in-house developed or acquired). If it does not reach a user base of several 100 million users (or 10's of billions of revenue) after a few years then they will scrap it.