Because of energy. Productivity going up means one person uses more machines, and as time goes, the machines do an ever increasing part of the job, because the energy feeding the machines is so much cheaper than human labour (in the order of 200 to 400 times cheaper).
This is not by chance that wage stagnation appeared in correlation with these events: US oil production peaked in 1970. Dollar convertibility to gold ended in 1971. Oil crisis came in 1974. OECD countries enter a permanent trend of public deficit in 1974. Unemployment soared in OECD countries at the same time.
As the ability to augment energy consumption became more and more capped by the ability to extract energy from the ground, workers gradually lost their capacity to obtain their part of the cake because it's always cheaper to put more capital than people at work, so far. The trend intensifies, nowadays we're talking of ending employment and of the necessity of basic income and similar tools.
Until the (unavoidable) end of cheap energy, that is... Then we'll be back to the ancient order of things, when a country GDP was entirely correlated to the size of its population.
This is not by chance that wage stagnation appeared in correlation with these events: US oil production peaked in 1970. Dollar convertibility to gold ended in 1971. Oil crisis came in 1974. OECD countries enter a permanent trend of public deficit in 1974. Unemployment soared in OECD countries at the same time.
As the ability to augment energy consumption became more and more capped by the ability to extract energy from the ground, workers gradually lost their capacity to obtain their part of the cake because it's always cheaper to put more capital than people at work, so far. The trend intensifies, nowadays we're talking of ending employment and of the necessity of basic income and similar tools.
Until the (unavoidable) end of cheap energy, that is... Then we'll be back to the ancient order of things, when a country GDP was entirely correlated to the size of its population.