I think Pinterest has other problems - mostly a market based on manipulating it - but hell so does google but google is further along in tech/services to increase quality.
What i really can't stand about pinterest is that even though it is a visual search - it requires an obscene amount of work from creators to be competitive - having to update your "pins" monthly and cycle them through and do A/B testing all the meanwhile others are stealing or borrowing your pins to enter those search terms/markets it creates a downward spiral - soon topics look spammy and only those who can afford to commit so much time/effort see the reward - then they turn around and start a business selling their idea.
No one looks at your boards anymore, they all search so people stuff their boards to find every variation of keyword and its starting to surface up to the search meaning searches get spammed by those who got there first rather than those most relevent.