I think the origins lie in the power of the medical profession with its germ theory philosophy, the pharmas and the food industry which all have a lot to answer for. They all help prop eachother up. I've not looked into this in any depth at all but I suppose besides Antibiotics the increasing use of 'convenient' foods full of c**p, depletion of minerals in the soil (since adding phosphorous to the soil in the 1970s), plus vaccinations, metals, damaged fats, increasing use of chemical, pollution, not having been breastfed, etc. all play their part. Also I suppose we live in a generally increasingly competitive stressful world which cares more about money than human beings! It's all a bit depressing isn't it!! :-0
We don't always help ourselves either but I think it's difficult to resist and tolerate the stresses of modern life.
I do think cleansing is important though and I think it has to be done continually throughout life based on natural cycles and a philosophy of prevention rather than looking for a cure.