Wetlands are areas that usually saturated with water , and water is the most important source of living for all living organisms
Since it's saturated with water, there are a wide varieties of plants that could survive the area.
Since there are a lot plants that could survive the area, a lot of herbivores can find their foods and decided to stay in that area.
Since a lot of herbivores reside in that area, it attract more carnivores.