Yeah, from BD student point of view, it might be more lucrative to go to west for research. But as you see, its for humanities, not every uni in west will provide money to research 'effect of Kazi Nazrul Islam's poetry on bengali literature and arts' for example.
Those who will pursue such subjects would get a free ride in public unis like DU. Private Unis don't have subs such as arts and humanities like Bengali lit. These subs are not popular and hence lack competition. Public unis boasts majority of such students.The highly meritorious ones in this field will easily get lucrative scholarships in western unis and many more can easily pursue it in public unis here where their competition will also be less. But then again as I said there will be some who will find it lucrative to study in India. Btw social sciences also includes subs like economics(?) for which opportunity in western unis will be abundant.