Mr banana sh** head, in bengal the admin and court languages were Persian during the mugual age the educated Muslims class leaning these languages to get jobs in govt. Bangla was spoken in casually on a daily basis at home and may be on the streets.
Then British came along and made english the administration language. Making large swathes of Muslim bengalis unemployed.
During the time of British the education budget for around 300 million people in the whole of South Asia was equal to small state in America, near New York.
Hindus happily embraced English, as it meant the down fall of Muslim prominence and Muslim for certain reasons resented English rule.
So lack of education, 31 major famines some of the worst being in bengal and constant malnourishment for 200 yrs.
During pre- independence bengali language received a boost of revival by notary works. It regained popularity in bengal.
During the creation of Pakistan changing the official language to urdu or English would have further alienated east bengals educated class. Making their mode of communication useless. During a time were resources constrained and east bengal was heavily economically exploited and majorly under funded by Central pak gov.
You have no idea of the reality or constraints. The complete garbage that comes out of you is annoying.