Soil that has been chemically treated has poor tilth. Healthy roots make healthy plants. Plants that cannot absorb the proper, balanced amounts of nutrients grow weak, unable to provide the necessary ingredients for proper stem and leaf development. Without a healthy root system, many plants will be easily lost to erosion, since there are no roots in the area to hold the soil in place. Soil with poor tilth erodes quickly.
Healthy plants resist drought, disease, and pests.
Try it yourself. Intentionally plant two seeds of anything in two different areas. It's an easily verifiable experiment. The Organic Conclusion Earthworms make plants resist drought, disease, and pests. If your plants are covered with pests, you need better soil.