It's the influence of money. We've allowed money to become just too important in our electoral politics. Both parties need railroad cars full of cash to run campaigns, and they both get this cash from the same sources, so you can't realistically expect their agendas to be all that much different. They both serve Big Money.
And what does Big Money want? It wants more money! Nobody gets to be a billionaire and then decides 'Well that's enough. I'll go away now and enjoy my wealth.' No, someone with a billion wants another billion to pile on top of it. They have the money to influence politics, so they do, hoping to do even better. And in fact 'investing' a few million in what has become no more than legalized bribery, that's the best investment you can make!
The Republicans, of course, like to demonize the poor. They would like you to believe that the ONLY reason for poverty is laziness, defects in character, unworthiness. They do this to distract us from the -real- crooks. It's the rich who are stealing us blind, not the poor.