Speaking for myself, not OP, and as someone who's criticised G+ strongly on numerous grounds:
Google+ started, at least, with a rather strong professional cachet. Its inaugural user cohort trended very strongly to Googlers, Xooglers, their immediate contacts, techies, and a number of folk with aligned interests.
And, unfortunately, SEO and marketing types. A very nearly fatal disease in a content-sharing community.
Google had a number of tremendous mis-steps. Privacy and confidentiality were very large among them, and I've little confidence that Vic Gundotra's G+ of 2012 could have executed on a professional-networking G+ successfully.
I think that with many of the very, very hard lessons Google's experienced, and I very sincerely hope has learned from, it could today.
Google could offer a G+ professional network which, at the very least, would benefit Google itself as a recruiting device. Possibly paired with other activities (women in STEM outreach, summer of code), and platforms (something Github-esque).
Google offering a general interest recruiting platform is probably a non-starter, in that it's a direct conflict of interest (Google would want the best candidates for itself), and in light of the illegal anti-poaching collusion case (still ongoing IIUC). Pity.
Google also don't need to directly monetise G+, an could avoid many of LinkedIn's more obnoxious practices.
