The rich are an easy target which allows people to project blame for their own personal failings and frustrations.
Nothing different from using blacks as an external target. Or Jews, immigrants, you know, 'those Arabs come here and, because they don't pay any taxes, they become millionaires and keep passing their business to family members every seven years.' The boss sleazed her way to the top, its not what you know its who you know, blah blah blah...
I'm not getting 'mine' because someone else is getting it and they're using an unfair advantage over me, I'm not successful because I don't kiss ass or because I'm too honest, blah blah blah.
You know, because there couldn't possibly be anything wrong with the way I'm going about it, there couldn't possibly be anything wrong with my expectations or thinking, there is certainly nothing wrong with me, so its just gotta be that my failings are the fault of someone else. Its just gotta be.