Because we're seeing a massive demographic change in this country as the white share of the population declines, which is exacerbated by coming in tandem with the political twilight of the largest and most polarized generation in a century occurring simultaneously as the next largest, and most diverse, generation begins to demand power. Further exacerbating is the aftershocks of a recession larger than anyone understood or cared to acknowledge, with rapid technological change making bubbles fiercer and more impenetrable than ever before.
That has completely nothing to do with it... it's just the internet. That's it. And Bernie.