Spain - Spanish, italy - Italian. Those who had self determination formed states along cultural and ethic identities and built up from there on.
Only countries that were colonalised and were subjugated into slavery lost their identities and cultural boundaries formed state borders through arbitrary lines. Which has caused cohesion problems in many countries.
At least bengalis stayed in touch with their root and reestablished their self determination.
Rohingya are refugees, in a stable region you expect Bangladesh to accept any group of people that have expelled for illegimate reason. That will open the flood gates with a poor country that has to worry about its own people first. Bangladesh is pressuring mymmar to accept their citizens back.
Biharis are people for first refused Bangladeshi citizen ship and claimed Pakistani citizen ship which pak gov promised but never acted on. Your Pakistani country is far more racist then Bangladeshi all that inbreeding kept your bloodline pure.
As you know Bangladesh have many different linages and admixtures. You inbred genetically deformed Troll.