I think events around 1971 have nothing to do with it. 1971 is simply when the impacts become visible. If I had to guess, would assume this timetable is based

I think events around 1971 have nothing to do with it. 1971 is simply when the impacts become visible. If I had to guess, would assume this timetable is based around the end of WW2. 1971-1945(end of WW2)=26 years. 26 years seems like a feasible amount of time for businesses to grow to the point where business owners don't need to share profits with employees to sustain growth. It's also around the amount of time when business owners welcomed their kids into company leadership positions. The post-war and somewhat "sheltered" children probably weren't as compassionate towards their fellow American (as their war-time parents were), leading to benefit reductions, lackluster pay-raises, and overall reduction of profit-sharing, etc. If you look around, it's pretty clear this has been compounding ever since.