Honey bees feed on the nectar of flowers. When a farmer practices bee farming or apiculture, the bees wander in its locality for nectar. Those bees feed on the nectar of flowers to flowers.

During each feeding, some of the pollen grains of the host flowers get attached to the bodies of the bees. When those bees feed on the other flowers, the pollen grains get transferred to them. As a result, there is cross-pollination in the crops of other farmers in the locality. This means more growth of crops and a higher yield. A higher yield results in greater income for farmers.

Thus, when a farmer practices bee farming, the income of other farmers in that locality also increases.

Here is the same question in a different wording.