The correct handlebar will put your hands in a position to support your upper body without putting strain on your neck and shoulders, and help balance your weight between the front and back wheels for proper handling. New shapes, like compact bends, offer improved ergonomics and control.
Many trend watchers point to the advent of compact-frame geometry in the 1990s. Those frames, still popular today, have sloping top tubes that accommodate a greater range of rider heights, allowing manufacturers to produce fewer sizes. Before those developments, most frames were designed with a rider’s ideal stem and saddle position in mind.