If Google+ were launching today, they might have a better chance. More people are interested in Facebook alternatives. At the time, Facebook had already supplanted MySpace and Google+ didn't offer anything attractive enough to switch again.
No point swapping Facebook for another advertising-driven social network in the same vein. If a company like Apple were running it and people were paying for it, that would be a different matter.
Google have contributed to privacy issues, e.g. with poor permission management.
I'd say the big difference with google is they can treat a social network as a loss leader. Google has other (far more profitable) forms of privacy invading revenue sources, facebook doesn't.
It's not a ideal solution however. If as a society we have decided social networks are important a not for profit, or decentralised federated scheme is probably the way to go.
Running a social website should be cheap enough that they don't need to be invasive. The company would be leaving money on the table as it where, but winning is worth enough that it's a good trade-off.
"If a company like Apple were running it and people were paying for it, that would be a different matter."
Oooh if only Apple did "social" apps well; they are famously not-so-great at doing them, I'm not sure where that comes from at root though.
Shooting from the hip: Maybe their intense internal secrecy translates into a worldview where the hyper-focus on the 1:1 relationship with their customer obscures their ability to see how their customers (and potential non-customers!) could interact; might even be dangerous.
