Because capex is what drives productivity and profits as opposed to the individual talent of labor in the majority of cases. US Steel went down the drain from its prime due to failure to invest in new technology.

While you may need to pay more for a high school educated worker who can read instruction manuals to operate heavy machinery than very common illiterate subsistence farmers. Notice that where productivity is based upon worker skill more than tools are still doing very well in wages. This is because the role of capital is more recruiting than direct productivity boosting. And well capital is good at self perpetuation.