My hypothesis is that working class wages are more sticky than white collar wages for reasons not strictly based on rationality.
I believe that Moravec's paradox explains why working class wages should be higher and white collar wages should be lower than at present.
https://en.wikipedia.org/wiki/Moravec's_paradox
Presently this is stalled because it is too counterintutive. People can't get their heads around the possibility of paying their gardeners and window cleaners more than their accountants or lawyers. That's the middle class version of The End of the World As We Know It.
This to me explains the existence of firms like Home Depot and the increasing popularity of prefabs.