Islam was around for a long time in Bangladesh, before British rule came in. British rule introduced freedom for anybody. The Bangladesh people stuck with their Islamic slavery idea, even though they practiced freedom to some extent. Then, as Bangladesh government gradually became its own thing, and the British had less and less influence, Islam gradually came back in force.
The Brits conquered Bengal in the 18th century, when the population was mostly Hindu. The Muslims gained the most from the British rule, as the Hindu Brahmin dominance was put to an end by the Europeans . Muslims became a majority in the eastern portions of Bengal somewhere in 1880 or 1890, after close to 100 years of British rule. Had Bengal remained under the local rulers, then it would have been Hindu by now.
And God gave them a chance to become His children by becoming the Christianity that the Brits brought to them. But they, in majority, rejected it. So God is giving them over to something worse.
Common law still works, even in Bangladesh. But they won't accept it, just like most Americans, British people, and Canadians.
