I did some research and discovered that there is an entire Wikipedia article dedicated to ghosts in Bengali culture. The article stated that ghosts are prominent in Bengali folk and fairy tales as well as modern literature. I found that one of the reasons that ghosts might be so common in Bengali literature is because Hindu beliefs are popular in the country. A reason there were many ghosts wandering the earth in the stories may be because if a person dies but the proper Hindu burial rituals are not complete the spirit cannot pass onto heaven and is left to haunt relatives until it is completed.
The Hindu influences also support the idea of an afterlife and many of the stories had karmic circumstances. For instance, in The Ghostly Wife and The Ghost-Brahman the ghosts are punished after being discovered to be taking over the life of a human.
The stories that included ghosts from the Untextbook were The Ghost-Brahman, The Ghostly Wife, The Story of a Brahmadaitya, and The Ghost who was Afraid of being Bagged. Depending on the tale the ghosts were either benevolent or malicious. And often times they were great field workers. The ghosts' characteristics reminded me of fairies from other folk tales. Also, in more than one story the ghost took the place of a human, this is a tiny bit similar to the idea of Changeling (a fairy taking a human and leaving behind a changeling).
The humans in many of these folktales feared the ghosts, but making friends with them often lead to great riches like in The Story of a Brahmadaitya. However, the ghosts were still a force to be reckoned with because they could take the life of a human with ease.
(Image in The Story of Brahmadaitya from the Untexbook.)