Why is only one soil type not ideal for growing all crops?

Answer 1

Different plants have different requirements: soil pH, drainage, organic content, even minerals in the soil all must be adjusted depending on what you're trying to grow. For example, blueberries need acidic soil. Other plants need alkaline soil. Some crops such as rice need standing water, while most others need well-drained soil. Some plants prefer very rich soil with a great deal of organic material, whereas others actually do better in sandy soils, for example. Some plants need certain minerals available in the soil, while others would be harmed by those minerals.
In general, most crops are actually pretty resiliant. But, if you are trying to get the most bushels per acre, it is best to amend your soil as much as possible for the requirements of the crop you are trying to grow. (Or, ideally, grow the crop that will grow best in the conditions you already have.)
Same goes for most garden plants: they'll survive in many locations in many types of soil, but they will grow, flower, and fruit much better if they have the specific soil requirements they need.

Answer 2

Crops are plants with different needs as far as soil goes. Some need better drainage, for instance. So soil that's good for one kind of crop isn't necessarily good for other crops.