1940 -1980 was a historical anomaly where the industries that grew at a tremendous pace needed a lot of employees to sustain that growth. It was a rare time that the worker had as much power as they did, and salaries reflected it. All of the things companies are eliminating now (pensions, healthcare) were things they invented post WWII to compete for workers.
Now, automation is creating most of the problem - it's siphoning off all of the low - low middle income jobs and creating two classes of people - tech workers who are doing well (overall, for NOW at least) and non-tech workers who, with few exceptions, are doing worse. Their prospects will diminish greatly over the next couple of decades as driving becomes automated - where are the lower rungs of the ladder going to be?