Agriculture is not the only thing humans do or settle for. Swamps are historically heavily inhabited by and sometimes even purposefully extended by humans specifically due to endemic biodiversity and ease of hunting and gathering. Also, sometimes because they offer fertile soils or refuge from other humans, and the waterways a strong source of orientation, food, and an artery for transport, trade and taxation. Examples off the top of my head: Bangladesh, Holland, Venice, Hanoi, Bangkok, Shanghai, Hangzhou, Angkor, Amazon, Sepik River of PNG...