The real issue here is globalization. In the post-WW2 years, US workers had a monopoly on labor provided to US firms, and thus were able to extract some of their firms' economic surplus (either through unionization or the threat of unionization). Company owners shared some of their profits with their workers because they had no other choice.

Now that trade borders are relatively open, companies have the option of looking elsewhere. US workers can no longer extract the surplus because if they attempt to, their company will simply relocate operations to a different country.

It's an either-or proposition: You can have free global trade, or you can have a job market that pays high wages to workers of average skill. You want both, but it's impossible; so we have to make a choice. We've chosen free global trade, and (as the article notes) there's a slow adjustment time in institutions. Figuring it began in the 1970's with Nixon opening up China, it took about 25 years to really be felt (in the dotcom bust, financial crisis and subsequent slow recovery).