That's because it's a lot more work: huge monoculture fields must be broken up into strips interspersed with bug resistant crops, crop rotation instead of fertilizers, etc.
A pre-modern agriculture can only support a pre-modern population. A return to pre-industrial methods would mean a return to working class Americans paying 40-50% of income for food, as was common in the early 20th century.
That’s a good point.
However, I was thinking along the lines of your house garden when I made my comment. Many people spray instead using natural remedies where they can.
For example, I was reading some time ago that you can create the richest garden imaginable if you dig up your garden and remove the dirt. Then interlace carbon and dirt when you put it all back.