It's been a lot longer than that. Here, take a look at this graph comparing productivity to average worker salary. They were completely in sync up through the 70s, then in the 80s worker salary flattened while productivity kept on the same increasing rate. 1981 was when Reagan took office and we started with "trickle down economics." Tax cuts for the wealthy and corporations that was supposed to "trickle down" to the worker. Conservatives still tout it today, but it's never done anything other than make rich people richer and screw the economy.

The problem is that those two lines are continuing on their respective paths, and businesses are expected to grow their productivity at that rate while keeping costs (including salaries) down. So we get squeezed to do more and more with less and less.