Because of the low quality. All the bots I've encountered were ridiculous. Like different "people" starting to follow me on Google+ (obviously intending to attract my attention so I would follow back) at the same moment and posting exactly the same (equal as string values) "thoughts" simultaneously. You can also find crowds of human-impersonating political bots posting exactly the same things on Twitter and in comments many times.

Perhaps this is for the same reason that Nigerian spammers can't spell? They are selecting for gullible targets.

"Why Do Nigerian Scammers Say They are From Nigeria?" by Cormac Herley (WEIS, 2012) https://www.microsoft.com/en-us/research/publication/why-do-...

Oh, I would assume a "real geek" was responsible for any bot activity on G+ before I'd assume some big orgs had bothered.