From the perspective of a plant... In soil, you have: silt, clay and sand. Plus other plants, fungi, worms, microorganisms, rocks, insects, animals, etc. Each plant needs different nutrients (nitrogen, phosphorus, potassium, and others), need different pH levels, can tolerate different salinity, etc. There might be different humidity, precipitation, wind speed, the water tables are different...

I guess all these differences translate into how the root must structurally develop to satisfy all those requirements and constraints.