There's Matt Cutts' long leave of absence, his departure, and the announcement that he's not really being replaced. A much lower volume of communication from Google on initiatives in the space (they used to talk endlessly about Panda, Penguin, etc). Amit's original reason for departure was "his next journey will involve philanthropy"..that seems to have changed.
My guess is that two things are driving the declining interest...
a) The marketshare battle is done. Google won. No competition.
b) Their various initiatives to push organic results down the fold (more ads, knowledge graph, various widgets, and so forth) has made the quality of the organic results not as important. Good enough is the target.