The main problem that Influencer Marketing is solving is that of attention.
From the standpoint of an ordinary buyer or consumer (applies to B2B or B2C), the WWW of products/services/things/stuff is vast and unfamiliar, and people simply cannot pay attention to everything. As such, Influencers can serve as a proxy for familiarity.
Even simple awareness should never be taken for granted by Marketers... As in the Age of the Social Graph, it's impossible to know precisely which networks (and people therein) exposure to your offering will catch the eye.
A Note on Influencers
One of the aspects that makes Influencer Marketing increasingly powerful and palatable is that many Influencers are extremely open (in their domain) to the new. The unfamiliar. The untested, untried, un-reviewed.
There is little Influencer currency to recommending ultra-familiar products. Conversely, the gain of introducing new, valuable products, services, ideas, contexts, fresh ways of looking at things are practically the definition of what makes someone worthy of influence in the first place.