Not all tournaments / organizations section people by gender.
However, as with many other cases, it has roots in the game being male-dominated early on, and either for social rules/values or personal interest reasons, women largely did not play, or were discouraged from playing. Women-only divisions aim to build interest in chess among women, or to create tournaments that are less dominated by male players who might have an advantage or longer span of experience/support on average.
In addition, some nations also just have rules that divide competitive games/sports of all kind into men and women divisions.
Latest Answers