From what I've seen in the book and heard in the podcast, Charlotte Bronte life's was very difficult, like most people during the Victorian Era. Bronte might of been born into a family with at least some amount of wealth, but she lived through a somewhat difficult childhood. Two of Bronte's siblings died in her childhood and what kind of author would like to bring up those memories?
From what I've read in the past authors will normally write autobiographies to be remembered. Everyone wants their story to live on through the ages which Bronte's surely has. Maybe remembering her past and having someone that was almost a sister to Jane Eyre, Helen Burns, die in the first part of the novel could almost be seen as a tribute. Authors have many reasons behind why they write their novels and I've been wondering why Bronte wrote hers.
This video only touches on why authors might write their autobiography, but it brings brings up some points to why Bronte might've wrote hers.