Actually, famed anarchist David Graeber has hypothesized that the capitalist class figured this one out a long time ago, and in fact designed the current neoliberal system to enable them to profit off cheap, indebted labor in preference to mechanizing, which (according to Marxian analyses, at least) could reduce their rate of profit.
Thus, the fight for labor rights becomes an important way of forcing the capitalists to mechanize and increase productivity.
Certainly if you look at some simple economics, it makes sense, as a hypothesis: a higher price of labor means a greater comparative advantage for machines, a lower price of labor makes massive sums of heavily exploited manpower easier to pay for than expensive mechanization infrastructure.
One may note also that one of the main driving forces of technology has been a relatively high cost of labor--it is theorized that one of the reasons Europeans had such an advantage against the Chinese and Indians in the 1800s, for example, was that they had developed systems not requiring large numbers of people.
Thus, the fight for labor rights becomes an important way of forcing the capitalists to mechanize and increase productivity.
Certainly if you look at some simple economics, it makes sense, as a hypothesis: a higher price of labor means a greater comparative advantage for machines, a lower price of labor makes massive sums of heavily exploited manpower easier to pay for than expensive mechanization infrastructure.