No paleogeneticist here but from what I know from : Andean people benefit from a genetic adaptation to high altitude and don't need coca leaves (Himalayan people also benefit from a different genetic adaptation). It does make work more enjoyable though.
Also, coca was reserved to higher classes in the past so laborers probably didn't have access to it. [1]
Also, coca was reserved to higher classes in the past so laborers probably didn't have access to it. [1]
[1] https://en.wikipedia.org/wiki/Coca#History