I suspect that the ignorance of farmers also stems from the fact that in times of taxes (the tenth crop yield or other forms), they have learned to exploit the soil in order to produce sufficient yields. Over the centuries, land has been cleared for agriculture and rootless soil is blown away by the wind. Unless the legacy of the forefathers helped teach that topsoil is precious and microbiology takes time, this knowledge has probably been lost over time. Knowlegge gets disrupted by crisis, war or other catastrophes, so I think where this happened, it might be that survival and fear could be responsible for losing knowledge.

I think that many effects build up over the years and then become visible much later. As we know, the effects in nature come about with a time lag. The farmers are probably the least responsible. Self-suppliers are likely to be exploitative only if their environment does the same and you are pushed into a system that sees profit first. Smallholders who cultivate their land by hand or with animals are caught in a vicious circle if they cannot draw on knowledge and joint efforts to prevent the devastation of areas.