The right hand may be the belle of the ball but the left hand is no dowdy Cinderella. The left hand is a fundamental part of piano music - literally, the fundamental is the root part of every note on the piano.
A strong left hand is crucial to successfully playing Bach, but what motivates a pianist to tackle the fiendish work of Godowsky who transcribed the already difficult Chopin preludes for the left hand alone? For some, such as Nicholas McCarthy who was born without his right hand, left-handed repertoire is the only option.