The main reasons:
1. Deregulation - The idea that corporations will police themselves is a fallacy
2. Destruction of our manufacturing base - primarily during the Reagan/Bush years, we saw the dismantling of our manufacturing base and the jobs shipped overseas so that corporate CEO's could pad their own pockets
3. GOP "Trickle down" economics policies - The idea that giving huge tax cuts to the wealthy and that the wealth will trickle down to the middle and working classes has one big problem, the wealthy don't reinvest so the money never trickles down. Since the Reagan era we have seen a growing disproportionality between the top 1% and the rest of the country.