Both Amazon and Google are sites that use English in their searches. The west is particularly advanced when it comes to using the internet to create pages or discuss things. Amazon is obviously dominated by goods and books retailed in the Western countries. Therefore the results you get back disproportionately represent the opinion of the West. Most westerners have little or know knowlege of the event, save the famine that followed in 1975, so it makes sense that they'd defer to the most simplistic title for the event, namely the "Bangladesh War". To use popular search engines and shop sites like Amazon to determine the title of the article is rather unencyclopedic. 
I want to add more to discuss 'genocide' here. Is what happened an incident of genocide. The George Washington University National Security Archives has some interesting declassified documents in this regard.