Some people are just jerks. That's the way of the world. However they tend to show up a lot in fiction. Because if every character were nice, there'd be no conflict. But sometimes, in order for a plot to work, or at least last as long as it does, practically everyone other than the main characters have to be antagonistic jerks. It's not that these characters are idiots, it's just that they're too mean to actually listen or help out with the conflict because it's beneath them.
Compare with Idiot Plot