Not all plants grow equally well in the same soil. Each plant has a preferred microbial, physical, and nutritional environment it thrives in.
When soil balance is optimized for our domesticated plants, the crop plants are healthier than the weeds. Now, the weeds have lower brix readings, and are more susceptible to disease and insects than the surrounding crop.
These lambsquarter plants were growing at the intersection of three fields, growing tomatoes, mixed salad greens, and peas. The last two crops can be very susceptible to aphids. There were no aphids to be found anywhere on the crops, while the lambsquarter was being consumed, as you can see.