Seems like a nice enough graphic to me. Perhaps the target audience is inclined to share socially and not necessary link. That's very normal.
9 linking root domains is decent and there are probably lower quality ones not being displayed by Open Site Explorer.
Pinterest would generate links but you usually won't see this flooding the results in Open Site Explorer, probably due to crawl depth of OSE and similar factors - most of the shares just aren't important enough to index.