The web has, to some extent, changed that. Blogs like this one and My Bangla Diary, and websites like So You Want To Learn A Language? make it easier, if you have the time, to find information and help with the language.
The wider question is how do those English speakers that learn a language after they leave school choose their subject.
Until then the role of the education system, and the weight of history, is more important. I chose to learn French and German in school, and then Italian in college, but the choice was around whether I would or would not learn the languages on offer, it wasn’t a choice between French and Bengali, German and Hindi or Italian and Mandarin.
After that there are a number of factors, most or all of which were mentioned on How To learn Any Language:
• Proximity – from the UK I’m more likely to visit France than India
• Economics – either directly, e.g. will I do business in India, if I do will I need an Indian language for this and if that’s the case will it be Hindi – the most spoken language in India, or Bengali (which is third) or will I stick with English (which is now second), or culturally, the dominance of Bollywood films and music is an effective way of spreading the language, both inside and outside India
• Culture – Bengali icons have their fans, starting with poet, author and playwright Rabindranath Tagore (who is the only Asian to win the Nobel prize for literature and was championed by W.E. Yeats) moving to film director Satyajit Ray (Martin Scorsese’s a fan) and ending with Ravi Shankar (George Harrison of The Beatles of course) but culturally Bengali has not really resonated with a Western audience for some time
But this isn’t meant to be a study of a language in terminal decline, though Bengali is I think at a curious juncture at the moment, slowly losing ground in India while east of the border they campaign for UN recognition.
And, unsurprisingly, I think language learning choices are much more personal than economics, more random than location and culture is something that only really comes into play after you begin learning a language.