because it may be feasible to cultivate only a limited variety of crops, or run a limited variety of cattle on particular lands, or because there is no perfect knowledge about what the market will do in the future, if there is great price volatility, climate uncertainty etc.
due to the potential for cultivating just a few crop types, raising only certain breeds of cattle on particular grounds, or due to insufficient knowledge about future market conditions, especially with high price fluctuations and uncertain climates.