Soils require time to develop. Rocks are broken down by various weathering processes to smaller particles, such as sand, silt and clay. The rate of weathering is often dependent upon climatic forces such as rain, heat, cold and wind. In time, plants become established only to decompose and be incorporated into the topsoil where there is an intimate mixture of organic and mineral matter. Nutrients are continually being released from minerals to the soil solution where they can be absorbed by plant roots. Over a long time period, the soil matures at a rate dependant upon localised conditions.
Within Scotland, soils are relatively 'young' being at most 10,000 years - the time elapsed since the end of the last Ice Age.
Links:
[1] https://www.hutton.ac.uk/staff/david-miller
[2] https://www.hutton.ac.uk/learning/exploringscotland/introduction
[3] https://www.hutton.ac.uk/introduction-soils