Vegetable gardening is not permanent landscaping. With few exceptions, vegetable plants are annuals, like bedding plants. They do their respective jobs within only a few months. When finished, they relinquish their space to different vegetable plants of a different season. More of the same will be in season again in a few months. Crop rotation is something to consider when that happens.
Crop rotation is standard procedure for field crops involving several acres of the same variety of vegetable. Some crops grow on the same land for a few years. Some change annually. With few exceptions of big perennial vegetable plants, none stay in the same location for too long. Some fields go fallow for a season without production. Most simply produce a different type of vegetable.
Vegetables that grow for too long in the same soil eventually deplete some of the nutrients that they use most. Different types of vegetables deplete different types of nutrients. Crop rotation allows soil that was depleted by one type of vegetable to be used by another type that does not mind the depletion. While slowly depleted of a new set of nutrients, soil recovers from previous depletion.
For example, a sunny side of a fence is an ideal spot to grow pole beans. It is tempting to grow them there annually. However, they do not perform as well for a second season, and are likely to be scant for a third year. However, tomatoes appreciate what beans do to the soil, and do not miss what they took from it. After tomatoes take what they want for a season, beans are ready to return.
Crop rotation also helps to disrupt the proliferation of host-specific pathogens that overwinter in the soil and decomposing plant parts.
Generally, new vegetable plants should not be of the same family as vegetable plants that they replace in a particular location. Beans, squash, okra or corn should be happy where tomatoes grew last year. Peppers and eggplants are of the same plant family as tomatoes, so are likely to crave what the tomatoes already depleted. They are also susceptible to some of the same pathogens.