From Time immemorial the fertile lands of Bengal has lured many traders and settlers. If you look at Bengal in the World map then you will find that not only it's the gateway to the Eastern parts of the Indian subcontinent but also has the shortest distance from any port (Bay of Bengal) to the Himalayan foothills (the Silk route). No wonder the traders have always found Bengal a convenient place to settle in, as carrying their goods through the sea and trading through Silk Route was way easier than any other place.
Apart from this huge geographical advantage The Ganges Bramhaputra Delta, the biggest of it's kind in the whole world, that had one of the most fertile land made Bengal another advantageous place. History has witnessed this land could grow almost all commercial crops like Indigo and opium so very profitably. Add to that the exquisite craftsmanship of Bengali weavers and their finest quality of Muslin which at one point of time made Bengal the foremost muslin exporter of the world.