Maybe the Less Wrong community doesn't display an unusual degree of nihilism and akrasia at all, or maybe it does but cogsci education has little to do with it.

I don't think it has anything to do with cogsci education. My own theory is that there are two basic reasons. First, nihilism and akrasia, often fueled by strong feelings of purposelessness and the impostor syndrome, are rampant among knowledge workers nowadays, especially in the academia. LW simply gathers together lots of such people who are unusually willing to talk about their situation openly here. Second, there is the selection effect for people who like to argue on the internet. It seems clear that this propensity is strongly correlated with all kinds of traits that tend to cause low achievement for smart people.

As for the causes of the widespread nihilism and akrasia among knowledge workers, I think it's a consequence of the general social trends of increasing bureaucratization, organizational decay, and institutionalized mendacity. Many people whose work should in principle be intellectually stimulating and providing a rich sense of accomplishment are instead trapped in a hell of pointless makework, Kafkaesque bureaucracy, Dilbertian chaos, and staggering mendacity and hypocrisy that one must endure and even actively participate in. (One can read much speculation on why the impostor syndrome is so rampant, but to me it seems that it often represents nothing but a realistic assessment of one's own situation, possibly coupled with an unrealistically favorable opinion about the situation of others.)

A deeper inquiry into these phenomena and their causes would unfortunately quickly lead to thorny ideological issues.