Why does S. E. Hinton use just her initials rather than her full name?

S. E. Hinton published The Outsiders in 1967. On the advice of her publisher, she used her initials instead of her full name, Susan Eloise, to forestall the inevitable criticism that female writers cannot write convincingly from the perspective of males. After it became known that S. E. Hinton was female, she continued to use S. E. Hinton as her professional name to draw a line between her public and private lives. Hinton has said in interviews and on her website that she values her privacy, and by publishing as "S. E." she can maintain separate identities as a public writer and private citizen.
Hinton's publisher in 1967 perhaps continued the nineteenth-century tradition of female writers masking their gender, apparently as a way to broaden their readership. J. K. Rowling's publisher is said to have given her the same advice upon publishing the Harry Potter novels. Mary Ann Evans published under the name George Eliot. Amantine Lucile Aurore Dupin wrote under the name George Sand. Emily Brontë published as Ellis Bell, Charlotte Brontë as Currer Bell, and Anne Brontë as Acton Bell.

Susan Eloise Hinton wrote The Outsiders when she was in high school and published her novel at the age of seventeen. Though her publishers were happy to print the novel, they were concerned her name might be a deterrent to potential readers. Especially for a story which deals so heavily with machismo, Viking Press felt a feminine name would discourage the target audience. As a result, Hinton chose to publish using her first and second initial alongside her surname. This decision is one many woman authors make, even today. Authors may fear having a feminine name implies their books are only for women, or only about topics which interest women. Of course, that's not necessarily true! Some women do write for a feminine audience, but many more are seeking to write to a more inclusive experience. Another famous author who chose to use a gender neutral pen name to prevent a gendered effect on book sales is J. K. Rowling, the author of the Harry Potter series.