Just conjecture: senior management in established corporations have stacked the payscales in their favor. I know senior managers in established corporations who have received ridiculously large bonuses and stock option grants for doing nothing other than what should ordinarily be expected of them for the benefit of the corporation, and their level of risk is so small relative to their reward. In some cases, the benefit to the corporation is of questionable value, yet excessively lavish compensation is granted. I suspect that some of these senior managers are greedier and more short-term oriented (I'll milk this baby as much as I can for my personal gain here and now) than their pre-yuppie predecessors. Maybe there was a greater sense of self-restraint and balance in depression and WWII-reared generations (or maybe just lower expectations and objectives)?

I think because, there's no reason to assume they would be - labor costs are still (mostly) driven by supply and demand. If gizmos and computers and internets increase a worker's productivity, the gains go to the business owners, while the worker still gets paid at whatever the labor market decides. (During the 60's era wage earners had some natural advantages: booming demand for labor, restricted supply since single-income households were the norm, less ability to send manufacturing or service jobs offshore.)

Higher top rates in the 60's era also meant some of that productivity gain in wealth went back to the average worker. The whole economy gained wealth from public investment in infrastructure, funding for education, healthcare research and so on. But around the late 70's, the tide started to turn towards lower taxes at the top. A few more trends got rolling at the same time: technology that made big productivity gains possible; entire manufacturing industries being sent overseas; the financial industry getting really interested in ways to move existing wealth from where it was, to their own pockets.

That makes it sound entirely bad, which it wasn't... those trends also led to a slew of innovative new companies, disruptions to established business practices, stock options as a way to share in the risk and reward, and lots of cool gadgets. It's more interesting now than in 1960. But there are a lot of workers getting the shaft, and don't necessarily need to be.

Because of the dismantling of the unions. I can not see any other factor being much more different than today, save for perhaps the deregulation of the banks where it seems a lot of wealth is concentrated, wealth which, I do think is a zero sum game as, whatever productivity might increase, it is taken away from some and given to some.

Someone mentioned the technological advances, but technology did not start in the 70s. We had the invention of energy before then, TV, radio, aeroplane, car, etc. So, I think that the period where the employees started sharing less of the gains seems to coincide with the dismantling of the unions, which, on a common sense approach also it makes sense as loosing your bargaining power you would expect would mean getting a worse deal.

because those employees did not produce the increase in productivity, technologists did.

The technologists and the entrenched oligopolists ate all of the surplus while the commoditized worker drones got nothing. Which is inline with free market theory. The wealth goes to the people who produce the wealth and the people who corner the market.