The soil which an earthworm ingests in converted through its intestines into more plant available forms.  The resulting earthworm poop has been processed several times and this results in a material which carries a higher nutrient load than the surrounding soil.

In comparison to soil, earth worms contains

5 times as much Nitrogen

7 times as much Potassium

2.5 times as much Magnesium

2 times as much Calcium