Of course, I wonder if PAMLFPR is no longer a socially relevant statistic. After all, there are a lot more women in the workforce currently, and (slightly) more men staying home. It's not as good an indication of who really needs work as it once was.
A sister-comment mentioned baby boomers-- there's a second index called prime age male labor force participation rate (PAMLFPR) that corrects for that by only looking at working-age men. We've gone down from 97% PAMLFPR in 1948 to 88% PAMLFPR in 2016.