I'm curious what hindsight causes you to believe would be the better move?

Anyway, at the time of partition, modern day Bangladesh was included as part of Pakistan (you seem to allude to this in your response, but it's not clear). Bangladesh broke off for numerous reasons, and (West) Pakistan didn't wish to let them go.

If you're asking why Bangladesh wasn't included from the get-go, I'm not sure. It was a pretty chaotic period (obviously). Also, what is often forgotten, is the "princely states" in British India were permitted to choose which country to go with (if any), which is something that led to the continuing dispute in Kashmir.

The two groups do not like each other at all. If the British just left without making clear borders, there would be huge disputes over territory. It would be the same situation as Iraq has been. Even today, the borders between them are heavily guarded.