it isn't a rule, it is aesthetics. A size 4 shoe looks too small, a size 12 looks too big. It is all about proportions and in what size the shoe looks best, they are trying to sell the shoe after all.
Just as most bikes you will see in any sales brochures, internet listings etc, are in the medium 55cm range as they just look better than a 47cm or 64cm bike.
it isn't a rule, it is aesthetics. A size 4 shoe looks too small, a size 12 looks too big. It is all about proportions and in what size the shoe looks best, they are trying to sell the shoe after all.
Just as most bikes you will see in any sales brochures, internet listings etc, are in the medium 55cm range as they just look better than a 47cm or 64cm bike.