I think the difference is three fold:
Up until recently, because the increases in productivity caused both increase in profit for capital and also increase in earnings for workers, the push for productivity benefited most of the population. In recent decades, almost all of the profit from increased productivity has gone to the top few percent, so people now are producing more but not reaping the benefit. This is the underlying economic change/instability/pressure.
Second, in recent decades, the increases in GDP etc. have also been accompanied by increases in volatility / decreases in stability: more volatile housing and stock markets, more corporate mergers and layoffs, less dependable pensions, etc.
So productivity goes up, workers don’t see much reward, and they see more insecurity.
And then lastly, wages for most workers have been “flat” for 4 decades but that’s only if you look at inflation in the aggregate. If you look at the cost of housing, higher education and health care, those have all gone up much more swiftly than wages for most Americans. And those areas are the core to long term prosperity, long term opportunity and long term stability. So wages are “flat” if you factor in being able to buy a bigger TV, but in terms of the foundations of long term quality of life, wages are actually relatively down for most Americans.
So, more productive, less quality of life, more insecurity. No wonder the millenials feel like they have it rough. They do in fact have it rough.
I’m a first wave Gen-X type and I put myself through the UC system undergrad by working and law school with borrowing that I could handle, but a person in my similar circumstances now could not do that. Relative to what I paid, and what I could earn, it requires more hours worked and more borrowing now, to what I consider a prohibitive extent. I was lucky in that I entered UC after CA was starting to cut back but before it got really horrendous, and before the relative value of low wage student jobs dropped through the floor.
It’s just not the same.