The handlebar is one of the bike parts that cannot be adjusted, even though shoulder width varies significantly between people. Narrow handlebars are better for speed and agility (mainly for road bikes) whereas wider handlebars are better for control and stability (mainly for mountain bikes).
Ideal narrow bars are considered 38-46cm and ideal wider handlebars 74-76cm. This is perfect for the male anatomy, with the average shoulder width being between 39-41 cm. However, the average shoulder width of a woman is 35-36cm. This means that an average woman (not a professional rider) uses handlebars too wide for her. As a result, there is a loss of speed, agility and comfort.
In order to accommodate for female anatomy as well as varied male anatomy, handlebars could have adjustable width the way the bike seats have an adjustable height.