Wages are the key—if you look closely at the numbers wages have not risen anywhere near the cost of living in the past few decades—particularly in the high cost of living areas.
This is a very sneaky way to lower a country’s standard of living.
I’d say it extends back to the 70s. The 90s saw a little reversal but it was short lived. The long term trend seems to start in the 70s and continues to this day.