Well, there’s this, and this to say you’re right. Had the minimum wage tracked in line with production, it would be ~$26 today. If it had tracked in line with inflation, it would probably be closer to $21.45.
That it’s been flatlined for so long means people working for minimum wage have been getting steady pay cuts for 50 years.
It also happens that this is one of the reasons social security is straining financially- they were able to predict the demographic bulge of the baby boomers well enough, but they weren’t able to predict that wages would be constrained in the way they have been- and wages are the basis for Social Security’s funding.