it might be because mangrove are of tremendous interest for local people.
In a mangrove you can collect construction wood, medicinal plants, prepare charcoal, hunt, fish, etc. But also the mangrove is the reproduction place for hundreds of crustaceans and fishes. When mangrove is cut, for example to have shrimp farms, local fishers income just collapse. And after a short while soils become unsuitable, often too salty. Of course the farms are bringing some money locally (actually mostly to the pocket of some rich urban peoples), but it does not last, and a lot of ressources are lost to the local peoples. From my observations in northern Java.
Sunderbans offer livelihood for millions of people besides nursery grounds for fish and migratory birds. These are highly productive zones on earth which in turn transforming the light energy into chemical energy and finally food for top carnivores. Having economical, medicinal and ecological importance to community as a whole growth and development of coastal regions...