Bangladesh is over populated as compared to many other countries. It is 8th most populous country. Not only that, its population density is also very high.
Earlier to 1980's there was no good practice of population control. Family planning methods were not available to people and they were not aware of them.
Most of the families had three or more children in the previous century. In the last two decades people have changed.
Many poor people wished to have more children so that they come in handy in their old age.
There was a lot of migration from other regions to Bangladesh due to its fertility and living conditions.
Population grew because of peaceful conditions prevailing the region.
The land is fertile, a lot of greenery around, so people settled down there.
There are a lot of rivers and generally civilizations settle down and develop near rivers and near fertile lands.