Populism and a perception that a more globally-connected world is concentrating the benefits of growth into the assets and control of a handful of individuals instead of "a rising tide lifting all boats." Also, the message that some politicians have been using ("trade agreements are evil!" "immigration is bad!" "the EU is making us abuse you!") has taken hold and people are pushing back against the perceived wrongs.
(I intentionally made no judgment call on the accuracy of these perceptions.)
The main driving factor is third-world immigration, and in particular the perception that mass immigration from the third world has had deleterious effects on the West, both economically and culturally.
What we're seeing right now is, I think, a preference cascade. For years people have been told that opposition to mass immigration is "racist" and have kept quiet about it, but now it's become more socially acceptable to talk about it.
Test of us non-postmodernists value an education system capable of producing competent elites, who in turn produce value for society (measure that how you like). By that measure, it's pretty apparent that Japan's universities are doing poorly.
And the Japanese agree with this, in case you missed it. Please stop with this nauseating pedantry.