It has to do with patent negotiations by the World Trade Organization and the Bangladesh status in the category of Least Developed Country.
LDCs are currently allowed to produce drugs off patent, but they are not allowed to distribute those drugs to any countries not also on the LDC list. The agreements come up for periodic review and I assume manufacturers don't want to do anything that might mess up their special exemption from international patent laws. If I remember right, they were to end in 2016 but it got extended ... don't remember the details.
Various distributers, on the other hand, don't have the huge investments or long term goals the manufacturers do, so they might be willing to export anyway. But that's exactly the point where the buyer has to begin questioning supply chain integrity.
If you're curious to know more, google
Bangladesh drug patent or maybe add
Least Developed Country, and/or
WTO to the searches.
BTW, glad to see you're finally swallowing your pill stash.
Edit: As for the currency/exchange issues and payment difficulty, it's a control-freak problem you see in many poor countries, and part of the reason they remain poor. For example, there is no good excuse why the Philippines lags so far behind its SE Asia neighbors in economic development except for their trade laws and foreign investment laws .... and the fact that 23 families hold major political control and exclusive franchise rights to entire industries.
In fact the words "Patent" and "Franchise" originated when the English Crown granted these exclusive rights .... in return for a cut of the action of course. Don't ever believe the BS that these legal peculiarities started out from ideological or philosophical principles.