Yeah, that Duolingo is a for-profit company that relies on volunteers to develop their courses is probably a mockery of someone, but it also explains why nobody has gifted them a Bengali course yet. On the other hand, people who learn a conlang are self-selected for willingness to spend a lot of time on something that's unlikely to gain them any material reward, so it's unsurprising some of them worked on a Duolingo course.

There are also almost three times as many Wikipedia articles in Esperanto as in Bengali, despite the Esperanto Wikipedia having less than a third the number of active users: https://meta.wikimedia.org/wiki/List_of_Wikipedias/Table2

It's not how many people speak it. It's how many people want to learn it as a second language. How many people would be in a position to want to learn Bengali if they don't already live there?