Other posts covered the reasons for the use of manual labor pretty well. Anecdotally, when i was in Central America i was astounded at how often they used human

Other posts covered the reasons for the use of manual labor pretty well. Anecdotally, when i was in Central America i was astounded at how often they used human labor for jobs like carving stone steps, digging holes, or carrying things. The equipment was available, but it was cheaper to hire 20 dudes to lug stuff around v. renting a truck. This may be a factor. Slightly off topic, but your comment reminded me how we have yet to find a technical workaround for infantry when it comes to invasion and occupation.