People get down and tired. They're frustrated and they look for something to make sense of the mood. Like there's some reason that isn't their fault. Race is a good catchall just about anyone can fall back on one way or another. They do it often enough and they become convinced it's true, whether they're acting pissy or not.

Not that race isn't an issue. But, there are lots of issues. Race is just an easy one for people to cry about. So, it gets used a lot.