There is a pretty strong correlation to your chart when you insert key dates from US labor laws and minimum wage laws. And if you look at it from a capitalism standpoint it makes sense. Companies produced cheap goods and made profit because they had very cheap labor without extra expenses tied to things like safety or limits to days/hours people could work. So when labor laws increased the costs to companies they then passed those costs onto consumers and drove up the price of goods. So the "value" of each dollar decreased as wage growth failed to keep pace with cost of good growth.

But I'm definitely not an economist. I'm a pattern guy and found these patterns interesting as they related to your chart.

1916, Congress passes a Child Labor Act (CLA)
1918, Supreme Court overturns CLA
1919, new CLA passed and this goes back and forth for a few years
1910-1929, Workers Compensation laws implemented across most states
1933, Congress passed the National Industrial Recovery Act (NIRA), gave the rights of unions to exist and negotiate
1935, Supreme Court overturns NIRA but Congress then passes National Labor Relations Act
1938, Congress passes the Fair Labor Standards Act (FLSA). This has minimum ages, minimum wages, and overtime if someone works beyond 40 hours in a week.
1963, Congress passes Equal Pay Act
1964, Congress passes Civil Rights Act
1970, Occupational Safety and Health Act